HI 


FOR 


SECONDARY  SCHOOLS 


BY   FRANCIS   M.   WALTERS,    A.M. 

PROFESSOR   OF   PHYSIOLOGY,    STATE   NORMAL 
SCHOOL,   WARRENSBURG,    MO. 


"  It  is  quite  possible  to  give  instruction  in  this  subject  in 
such  a  manner  as  not  only  to  confer  knowledge  which  is 
useful  in  itself,  but  to  serve  the  purpose  of  a  training  in 
accurate  observation,  and  in  the  methods  of  reasoning  of 
physical  science."  —  Huxley. 


D.    C.    HEATH    &    CO.,    PUBLISHERS 

BOSTON        NEW   YORK        CHICAGO 


COPYRIGHT,  1909, 
Bv  FRANCIS  M.  WALTERS. 


1F3 


PREFACE 

THE  aim  in  the  preparation  of  this  treatise  on  the  human 
body -has  been,  first,  to  set  forth  in  a  teachable  manner  the 
actual  science  of  physiology ;  and  second,  to  present  the 
facts  of  hygiene  largely  as  applied  physiology.  The  view 
is  held  that  "right  living"  consists  in  the  harmonious  ad- 
justment of  one's  habits  to  the  nature  and  plan  of  the  body, 
and  that  the  best  preparation  for  such  living  is  a  correct 
understanding  of  the  physical  self.  It  is  further  held  that 
the  emphasizing  of  physiology  augments  in  no  small  degree 
the  educative  value  of  the  subject,  greater  opportunity 
being  thus  afforded  for  exercise  of  the  reasoning  powers 
and  for  drill  in  the  modus  operandi  of  natural  forces.  In 
the  study  of  physiology  the  facts  of  anatomy  have  a  place, 
but  in  an  elementary  course  these  should  be  restricted  to 
such  as  are  necessary  for  revealing  the  general  structure 
of  the  body. 

Although  no  effort  has  been  spared  to  bring  this  work 
within  the  comprehension  of  the  pupil,  its  success  in  the 
classroom  will  depend  largely  upon  the  method  of  handling 
the  subject  by  the  teacher.  It  is  recommended,  there- 
fore, that  the  relations  which  the  different  organs  and 
processes  sustain  to  each  other,  and  to  the  body  as  a  whole, 
be  given  special  prominence.  The  pupil  should  be  im- 
pressed with  the  essential  unity  of  the  body  and  should 
see  in  the  diversity  of  its  activities  the  serving  of  a  common 
purpose.  In  creating  such  an  impression  the  introductory 

2056774 


jv  PREFACE 

paragraphs  at  the  beginning  of  many  of  the  chapters  and 
the  summaries  throughout  the  book,  as  well  as  the  general 
arrangement  of  the  subject-matter,  will  be  found  helpful. 

Since  the  custom  largely  prevails  of  teaching  physiology 
in  advance  of  the  sciences  upon  which  it  rests  —  biology, 
physics,  and  chemistry  —  care  should  be  exercised  to  de- 
velop correct  ideas  of  the  principles  and  processes  derived 
from  these  sciences.  Too  much  latitude  has  been  taken 
in  the  past  in  the  use  of  comparisons  and  illustrations  drawn 
from  "  everyday  life."  To  teach  that  the  body  is  a  "  house," 
"  machine,"  or  "  city  "  ;  that  the  nerves  carry  "  messages  "  ; 
that  the  purpose  of  oxygen  is  to  "burn  up  waste";  that 
breathing  is  to  "  purify  the  blood,"  etc.,  may  give  the  pupil 
phrases  which  he  can  readily  repeat,  but  teaching  of  this 
kind  does  not  give  him  correct  ideas  of  his  body. 

The  method  of  teaching,  however,  that  uses  the  pupil's 
experience  as  a  basis  upon  which  to  build  has  a  value  not 
to  be  overlooked.  The  fact  that  such  expressions  as  those 
quoted  above  are  so  easily  remembered  proves  the  value 
of  connecting  new  knowledge  with  the  pupil's  experience. 
But  the  inadequacy  of  this  experience  must  be  recognized 
and  taken  into  account.  The  concepts  of  the  average 
pupil  are  entirely  too  indefinite  and  limited  to  supply  the 
necessary  foundation  for  a  science  such  as  physiology. 
Herein  lies  the  great  value  of  experiments  and  observa- 
tions. They  supplement  the  pupil's  experience,  and  in- 
crease both  the  number  and  definiteness  of  his  concepts. 
No  degree  of  success  can  be  attained  if  this  phase  of  the 
study  is  omitted. 

The  best  results  in  physiology  teaching  are  of  course 
attained  where  laboratory  work  is  carried  on  by  the  pupils, 
but  where  this  cannot  be  arranged,  class  experiments  and 
observations  must  suffice.  The  Practical  Work  described 


PREFACE  V 

at  the  close  of  most  of  the  chapters  is  mainly  for  class  pur- 
poses. While  these  serve  a  necessary  part  in  the  develop- 
ment of  the  subject,  it  is  not  essential  that  all  of  the 
experiments  and  observations  be  made,  the  intention  being 
to  provide  for  some  choice  on  the  part  of  the  teacher.  A 
note-book  should  be  kept  by  the  pupil. 

To  adapt  the  book  to  as  wide  a  range  of  usefulness  as 
possible,  more  subject-matter  is  introduced  than  is  usually 
included  in  an  elementary  course.  Such  portions,  how- 
ever, as  are  unessential  to  a  proper  understanding  of  the 
body  by  the  pupil  are  set  in  small  type,  to  be  used  at  the 
discretion  of  the  teacher. 

The  use  of  books  of  reference  is  earnestly  recommended. 
For  this  purpose  the  usual  high  school  texts  may  be  em- 
ployed to  good  advantage.  A  few  more  advanced  works 
should,  however,  be  frequently  consulted.  For  this  pur- 
pose Martin's  Human  Body  (Advanced  Course),  Rettger's 
Advanced  Lessons  in  Physiology,  Thornton's  Human  Physi- 
ology, Huxley's  Lessons  in  Elementary  Physiology,  Howell's 
A  Text-book  of  Physiology,  Hough  and  Sedg wick's  Hygiene 
and  Sanitation,  and  Pyle's  Personal  Hygiene  will  be  found 
serviceable. 

In  the  preparation  of  this  work  valuable  assistance  has 
been  rendered  by  Dr.  C.  N.  McAllister,  Department  of 
Psychology,  and  by  Professor  B.  M.  Stigall,  Department 
of  Biology,  along  the  lines  of  their  respective  specialties, 
and  in  a  more  general  way  by  President  W.  J.  Hawkins 
and  others  of  the  Warrensburg,  Missouri,  State  Normal 
School.  Expert  advice  from  Professor  S.  D.  Magers,  In- 
structor in  Physiology  and  Bacteriology,  State  Normal 
School,  Ypsilanti,  Michigan,  has  been  especially  helpful, 
and  many  practical  suggestions  from  the  high  school 
teachers  of  physiology  of  Kansas  City,  Missouri,  Professor 


vi  PREFACE 

C.  H.  Nowlin,  Central  High  School,  Dr.  John  W.  Scott, 
Westport  High  School,  'and  Professor  A.  E.  Shirling, 
Manual  Training  High  School,  all  of  whom  read  both 
manuscript  and  proofs,  have  been  incorporated.  Consid- 
erable material  for  the  Practical  Work,  including  the  res- 
piration experiment  (page  101)  and  the  reaction  time 
experiment  (page  323),  were  contributed  by  Dr.  Scott. 
Professor  Nowlin's  suggestions  on  subject-matter  and 
methods  of  presentation  deserve  special  mention.  To 
these  and  many  others  the  author  makes  grateful 
acknowledgment. 

F.  M.  W. 

MISSOURI  STATE  NORMAL  SCHOOL, 
SECOND  DISTRICT,  May  i,  1909. 


TABLE    OF   CONTENTS 
PART   I      ' 

THE   VITAL   PROCESSES 

CHAPTER  PAGE 

I.     INTRODUCTION i 

II.    GENERAL  VIEW  OF  THE  BODY 4 

III.  THE  BODY  ORGANIZATION 13 

IV.  THE  BLOOD 24 

V.    THE  CIRCULATION  .                 40 

VI.    THE  LYMPH  AND  ITS  MOVEMENT  THROUGH  THE  BODY  65 

VII.    RESPIRATION 76 

VIII.     PASSAGE  OF  OXYGEN  THROUGH  THE  BODY    .        .        .  104 

IX.      FOODS  AND   THE  THEORY  OF   DIGESTION           .            .            .  I  17 

X.     ORGANS  AND  PROCESSES  OF  DIGESTION          .        .        .138 

XL    ABSORPTION,  STORAGE,  AND  ASSIMILATION    .        .        .173 

XII.     ENERGY  SUPPLY  OF  THE  BODY 186 

XIII.  GLANDS  AND  THE  WORK  OF  EXCRETION       .        .        .  197 
SUMMARY  OF  PART  I     .        .        .        .        .        .'....  215 

PART    II 

MOTION,   COORDINATION,   AND   SENSATION 

XIV.  THE  SKELETON 216 

XV.    THE  MUSCULAR  SYSTEM 243 

XVI.     THE  SKIN 264 


viii  TABLE   OF   CONTENTS 

CHAPTER  PAGE 

XVII.  STRUCTURE  OF  THE  NERVOUS  SYSTEM  .  .  .  279 

XVIII.  PHYSIOLOGY  OF  THE  NERVOUS  SYSTEM  .  .  .  304 

XIX.  HYGIENE  OF  THE  NERVOUS  SYSTEM  .  .  .  .  324 

XX.  PRODUCTION  OF  SENSATIONS 338 

XXI.  THE  LARYNX  AND  THE  EAR 350 


XXII.     THE  EYE 


370 


XXIII.    THE  GENERAL  PROBLEM  OF  KEEPING  WELL     .        .  392 

SUMMARY  OF  PART  II 42 ! 

APPENDIX 422 

INDEX         . 423 


PHYSIOLOGY   AND    HYGIENE 
PART   I:    THE  VITAL   PROCESSES 

CHAPTER  I 
INTRODUCTION 

To  derive  strength  equal  to  the  daily  task ;  to  experience 
the  advantages  of  health  and  avoid  the  pain,  inconvenience, 
and  danger  of  disease ;  to  live  out  contentedly  and  use- 
fully the  natural  span  of  life :  these  are  problems  that 
concern  all  people.  They  are,  however,  but  different 
phases  of  one  great  problem  —  the  problem  of  properly 
managing  or  caring  for  the  body.  To  supply  knowledge 
necessary  to  the  solution  of  this  problem  is  the  chief  reason 
why  the  body  is  studied  in  our  public  schools. 

Divisions  of  the  Subject.  —  The  body  is  studied  from 
three  standpoints :  structure,  use  of  parts,  and  care  or 
management.  This  causes  the  main  subject  to  be  con- 
sidered under  three  heads,  known  as  anatomy,  physiology, 
and  hygiene. 

Anatomy  treats  of  the  construction  of  the  body  —  the 
parts  which  compose  it,  what  they  are  like,  and  where  lo- 
cated. Its  main  divisions  are  known  as  gross  anatomy  and 
histology.  Gross  anatomy  treats  of  the  larger  structures 
of  the  body,  while  histology  treats  of  the  minute  structures 
of  which  these  are  composed  —  parts  too  small  to  be  seen 
with  the  naked  eye  and  which  have  to  be  studied  with  the 
aid  of  the  microscope. 

i 


2  THE   VITAL  PROCESSES 

Physiology  treats  of  the  function,  or  use,  of  the  different 
parts  of  the  body  —  the  work  which  the  parts  do  and  how 
they  do  it  —  and  of  their  relations  to  one  another  and  to 
the  body  as  a  whole. 

Hygiene  treats  of  the  proper  care  or  management  of  the 
body.  In  a  somewhat  narrower  sense  it  treats  of  the 
"  laws  of  health."  Hygiene  is  said  to  be  personal,  when 
applied  by  the  individual  to  his  own  body ;  domestic,  when 
applied  to  a  small  group  of  people,  as  the  family;  and 
public,  or  general,  when  applied  to  the  community  as  a 
whole  or  to  the  race. 

The  General  Aim  of  Hygiene.  —  There  are  many  so-called 
laws  of  health,  and  for  these  laws  it  is  essential  in  the 
management  of  the  body  to  find  a  common  basis.  This 
basic  law,  suggested  by  the  nature  of  the  body  and  condi- 
tions that  affect  its  well-being,  may  be  termed  the  Law  of 
Harmony:  The  mode  of  living  must  harmonize  with  the 
plan  of  the  body.  To  live  properly  one  must  supply  the 
conditions  which  his  body,  on  account  of  its  nature  and 
plan,  requires.  On  the  other  hand,  he  must  avoid  those 
things  and  conditions  which  are  injurious,  i.e.,  out  of 
harmony  with  the  body  plan.  To  secure  these  results, 
it  is  necessary  to  determine  what  is  and  what  is  not 
in  harmony  with  the  plan  of  the  body,  and  to  find  the 
means  of  applying  this  knowledge  to  the  everyday  prob- 
lems of  living.  Such  is  the  general  aim  of  hygiene. 
Stated  in  other  words :  Hygiene  has  for  its  general  aim 
the  bringing  about  of  an  essential  harmony  between  the 
body  and  the  things  and  conditions  that  affect  it.1 


1  The  body  is  affected  by  what  it  does  (exercise,  work,  sleep) ,  by  things  taken 
into  it  (food,  air,  drugs),  and  by  things  outside  of  it  (the  house  in  which  one  lives, 
climate,  etc.).  That  phase  of  hygiene  which  has  for  its  object  the  making  of  the 
surroundings  of  the  body  healthful  is  known  as  sanitation. 


INTRODUCTION  3 

Relation  of  Anatomy  and  Physiology  to  the  Study  of 
Hygiene.  —  If  the  chief  object  in  studying  the  body  is  that 
of  learning  how  to  manage  or  care  for  it,  and  hygiene 
supplies  this  information,  why  must  we  also  study  anatomy 
and  physiology  ?  The  answer  to  this  question  has  already 
been  in  part  suggested.  In  order  to  determine  what 
things  and  conditions  are  in  harmony  with  the  plan  of  the 
body,  we  must  know  what  that  plan  'is.  This  knowledge  is 
obtained  through  a  study  of  anatomy  and  physiology. 
The  knowledge  gained  through  these  subjects  also  renders 
the  study  of  hygiene  more  interesting  and  valuable.  One 
is  enabled  to  see  why  and  hoiv  obedience  to  hygienic  laws 
benefits,  and  disobedience  to  them  injures,  the  body. 
This  causes  the  teachings  of  hygiene  to  be  taken  more 
seriously  and  renders  them  more  practical.  In  short, 
anatomy  and  physiology  supply  a  necessary  basis  for  the 
study  of  hygiene. 

Advantages  of  Properly  Managing  the  Body.  —  One 
result  following  the  mismanagement  of  the  body  is  loss  of 
health.  But  attending  the  loss  of  health  are  other  results 
which  are  equally  serious  and  far-reaching.  Without  good 
health,  people  fail  to  accomplish  their  aims  and  ambitions 
in  life;  they  miss  the  joy  of  living;  they  lose  their  ability 
to  work  and  become  burdens  on  their  friends  or  society. 
The  proper  management  of  the  body  means  health,  and  it 
also  means  the  capacity  for  work  and  for  enjoyment.  Not 
only  should  one  seek  to  preserve  his  health  from  day  to 
day,  but  he  should  so  manage  his  body  as  to  use  his 
powers  to  the  best  advantage  and  prolong  as  far  as  possi- 
ble the  period  during  which  he  may  be  a  capable  and 
useful  citizen. 


CHAPTER   II 
GENERAL  VIEW  OF  THE  BODY 

External  Divisions.  —  Examined  from  the  outside,  the 
body  presents  certain  parts,  or  divisions,  familiar  to  all. 
The  main,  or  central,  portion  is  known  as  the  trunk,  and 
to  this  are  attached  the  head,  the  upper  extremities,  and 
the  loiver  extremities.  These  in  turn  present  smaller 
divisions  which  are  also  familiar.  The  upper  part  of  the 
trunk  is  known  as  the  thorax,  or  chest,  and  the  lower  part 
as  the  abdomen.  The  portions  of  the  trunk  to  which  the 
arms  are  attached  are  the  shoulders,  and  those  to  which 
the  legs  are  joined  are  the  hips,  while  the  central  rear 
portion  between  the  neck  and  the  hips  is  the  back.  The 
fingers,  the  hand,  the  wrist,  the  forearm,  the  elbow,  and 
the  upper  arm  are  the  main  divisions  of  each  of  the  upper 
extremities.  The  toes,  the  foot,  the  ankle,  the  lower  leg, 
the  knee,  and  the  thigh  are  the  chief  divisions  of  each  of 
the  lower  extremities.  The  head,  which  is  joined  to  the 
trunk  by  the  neck,  has  such  interesting  parts  as  the  eyes, 
the  ears,  the  nose,  the  jaws,  the  cheeks,  and  the  mouth. 
The  entire  body  is  inclosed  in  a  double  covering,  called 
the  skin,  which  protects  it  in  various  ways. 

The  Tissues.  —  After  examining  the  external  features  of 
the  body,  we  naturally  inquire  about  its  internal  structures. 
These  are  not  so  easily  investigated,  and  much  which  is  of 
interest  to  advanced  students  must  be  omitted  from  an 
elementary  course.  We  may,  however,  as  a  first  step  in 
this  study,  determine  what  kinds  of  materials  enter  into 

4 


GENERAL   VIEW   OF  THE   BODY  5 

the  construction  of  the  body.  For  this  purpose  the  body 
of  some  small  animal  should  be  dissected  and  studied. 
(See  observation  at  close  of  chapter.)  The  different 
materials  found  by  such  a  dissection  correspond  closely  to 
the  substances,  called  tissues,  which  make  up  the  human 
body.  The  main  tissues  of  the  body,  as  ordinarily  named, 
are  the  muscular  tissue,  the  osseous  tissue,  the  connective 
tissue,  the  nervous  tissue,  the  adipose  tissue,  the  cartilagi- 
nous tissue,  and  the  epithelial  and  glandular  tissue.  Most 
of  these  present  different  varieties,  making  all  together 
some  fifteen  different  kinds  o.f  tissues  that  enter  into  the 
construction  of  the  body.1 

General  Purposes  of  the  Tissues.  —  The  tissues,  first  of 
all,  form  the  body.  As  a  house  is  constructed  of  wood, 
stone,  plaster,  iron,  and  other  building  materials,  so  is  the 
body  made  up  of  its  various  tissues.  For  this  reason  the 
tissues  have  been  called  the  building  materials  of  the  body. 

In  addition  to  forming  the  body,  the  tissues  supply  the 
means  through  which  its  work  is  carried  on.  They  are 
thus  the  zvorking  materials  of  the  body.  In  serving  this 
purpose  the  tissues  play  an  active  r61e.  All  of  them 
must  perform  the  activities  of  growth  and  repair,  and 
certain  ones  (the  so-called  active  tissues)  must  do  work 
which  benefits  the  body  as  a  whole. 

Purposes  of  the  Different  Tissues.  —  In  the  construction 
of  the  body  and  also  in  the  work  which  it  carries  on,  the 
different  tissues  are  made  to  serve  different  purposes. 
The  osseous  tissue  is  the  chief  substance  in  the  bony 
framework,  or  skeleton,  while  the  muscular  tissue  produces 
the  different  movements  of  the  body.  The  connective 

1  When  classified  according  to  their  essential  structure,  the  tissues  fall  into  four 
main  groups :  epithelial  and  glandular  tissue,  muscular  tissue,  nervous  tissue, 
and  connective  tissue.  According  to  this  system  the  osseous,  cartilaginous,  and 
adipose  tissues  are  classed  as  varieties  of  connective  tissue.  See  page  18. 


6  THE   VITAL   PROCESSES 

tissue,  which  is  everywhere  abundant,  serves  the  general 
purpose  of  connecting  the  different  parts  together.  Carti- 
laginous tissue  forms  smooth  coverings  over  the  ends  of 
the  bones  and,  in  addition  to  this,  supplies  the  necessary 
stiffness  in  organs  like  the  larynx  and  the  ear.  The 
nervous  tissue  controls  the  body  and  brings  it  into  proper 
relations  with  its  surroundings,  while  the  epithelial  tissue 
(found  upon  the  body  surfaces  and  in  the  glands)  supplies 
it  with  protective  coverings  and  secretes  liquids.  The  adi- 
pose tissue  (fat)  prevents  the  too  rapid  escape  of  heat  from 
the  body,  supplies  it  with  nourishment  in  time  of  need, 
and  forms  soft  pads  for  delicate  organs  like  the  eyeball. 

Properties  of  the  Tissues.  —  If  we  inquire  how  the  tissues 
are  able  to  serve  such  widely  different  purposes,  we  find 
this  answer.  The  tissues  differ  from  one  another  both  in 
composition  and  in  structure  and,  on  this  account,  differ  in 
their  properties.1  Their  different  properties  enable  them 
to  serve  different  purposes  in  the  body.  Somewhat  as 
glass  is  adapted  by  its  transparency,  hardness,  and  tough- 
ness to  the  use  made  of  it  in  windows,  the  special  proper- 
ties of  the  tissues  adapt  them  to  the  kinds  of  service  which 
they  perform.  Properties  that  adapt  tissues  to  their  work 
in  the  body  are  called  essential  properties.  The  most  im- 
portant of  these  essential  properties  are  as  follows : 

i.  Of  osseous  tissue,  hardness,  stiffness,  and  toughness. 
2.  Of  muscular  tissue,  contractility  and  irritability.  3.  Of 
nervous  tissue,  irritability  and  conductivity.  4.  Of  carti- 
laginous tissue,  stiffness  and  elasticity.  5.  Of  connective 
tissue,  toughness  and  pliability.  6.  Of  epithelial  tissue, 
ability  to  resist  the  action  of  external  forces  and  power  to 
secrete. 

1  The  properties  of  substances  are  the  qualities  or  characteristics  (color,  weight, 
etc.)  by  means  of  which  they  are  recognized. 


GENERAL   VIEW    OF   THE    BODY 


Tissue  Groups.  —  In  the  construc- 
tion of  the  body  the  tissues  are 
grouped  together  to  form  its  various 
divisions  or  parts.  A  group  of  tissues 
which  serves  some  special  purpose  is 
known  as  an  organ.  The  hand,  for 
example,  is  an  organ  for  grasping 
(Fig.  i).  While  the  different  organs 
of  the  body  do  not  always  contain 
the  same  tissues,  and  never  contain 
them  in  the  same  proportions,  they 
do  contain  such  tissues  as  their  work 
requires  and  these  have  a  special 
arrangement  —  one  adapted  to  the 
work  which  the  organs  perform. 

In  addition  to  forming  the  organs, 
the  tissues  are  also  grouped  in  such 
a  manner  as  to  provide  supports  for 
organs  and  to  form  cavities  in  which 
organs  are  placed.  The  various  cavi- 
ties of  the  body  are  of  particular 
interest  and  importance.  The  three 
largest  ones  are  the  cranial  cavity, 
containing  the  brain;  the  thoracic 
cavity,  containing  the  heart  and  the 
lungs ;  and  the  abdominal  cavity, 

containing  the  stomach,  the  liver,  the       FlG-    I-  ~~  Han<* 
....  1-1        •  forearm,      showing      me 

intestines,  and  other  important  organs  grouping  of  musjar  and 

(Fig.     2).         Smaller    cavities     serving   connective    tissues  in    the 

different  purposes  are  also  found.         organ  for  grasPing- 

Organs  and  Systems.  —  The  work  of  the  body  is  carried 
on  by  its  various  organs.  Many,  in  fact  the  majority,  of 
these  organs  serve  more  than  one  purpose.  The  tongue 


and 

showing      the 


THE   VITAL   PROCESSES 


Cranial_ 
cavity 


Thoracic  ///Lungs 

cavity 

Ifft    . 

/Heart    } 


Abdominal_ 
cavity 


FIG.  2.  — Diagram  of  a  lengthwise  section  of  the  body  to  show  its 
large  cavities  and  the  organs  which  they  contain. 


GENERAL    VIEW    OF   THE    BODY  9 

is  used  in  talking,  in  masticating  the  food,  and  in  swallow- 
ing. The  nose  serves  at  least  three  distinct  purposes. 
The  mouth,  the  arms,  the  hands,  the  feet,  the  legs,  the 
liver,  the  lungs,  and  the  stomach  are  also  organs  that  serve 
more  than  one  purpose.  This  introduces  the  principle  of 
economy  into  the  construction  of  the  body  and  diminishes 
the  number  of  organs  that  would  otherwise  be  required. 

The  various  organs  also  combine  with  one  another  in 
carrying  on  the  work  of  the  body.  An  illustration  of  this 
is  seen  in  the  digestion  of  the  food  —  a  process  which 
requires  the  combined  action  of  the  mouth,  stomach,  liver, 
intestines,  and  other  organs.  A  number  of  organs  working 
together  for  the  same  purpose  form  a  system.  The  chief 
systems  of  the  body  are  the  digestive  system,  the  cir- 
culatory system,  the  respiratory  system,  the  muscular  sys- 
tem, and  the  nervous  system. 

The  Organ  and  its  Work.  —  A  most  interesting  question 
relating  to  the  work  of  the  organ  is  this :  Does  the  organ 
work  for  its  own  benefit  or  for  the  benefit  of  the  body  as  a 
whole  ?  Does  the  hand,  for  example,  grasp  for  itself  or  in 
order  that  the  entire  body  may  come  into  possession  ?  Only 
slight  study  is  sufficient  to  reveal  the  fact  that  each  organ 
performs  a  work  which  benefits  the  body  as  a  whole.  In 
other  words,  just  as  the  organ  itself  is  a  part  of  the  body, 
the  work  which  it  does  is  a  part  of  the  necessary  work 
which  the  body  has  to  do. 

But  in  working  for  the  general  good,  or  for  the  body  as 
a  whole,  each  organ  becomes  a  sharer  in  the  benefits  of 
the  work  done  by  every  other  organ.  While  the  hand 
receives  only  a  little  of  the  nourishment  contained  in  the 
food  which  it  places  in  the  mouth  or  of  the  heat  from 
fuel  which  it  places  on  the  fire,  it  is  aided  and  supported 
by  the  work  of  all  the  other  organs  of  the  body  —  eyes, 


I0  THE   VITAL   PROCESSES 

feet,  brain,  heart,  etc.  The  hand  does  not  and  cannot 
work  independently  of  the  other  organs.  It  is  one  of  the 
partners  in  a  very  close  combination  where,  by  doing  a  par- 
ticular work,  it  shares  in  the  profits  of  all.  What  is  true  of 
the  hand  is  true  of  every  other  organ  of  the  body. 

An  Organization.  —  The  relations  which  the  different 
organs  sustain  to  each  other  and  to  the  body  as  a  whole 
suggest  the  possibility  of  classifying  the  body  as  an  organ- 
ization. This  term  is  broadly  applied  to  a  variety  of  com- 
binations. An  organization  is  properly  defined  as  any 
group  of  individuals  which,  in  working  together  for  a 
common  purpose,  practices  the  division  of  labor.  This 
definition  will  be  better  understood  by  considering  a  few 
familiar  examples. 

A  baseball  team  is  an  organization.  The  team  is  made 
up  of  individual  players.  These  work  together  for  the 
common  purpose  of  winning  games.  They  practice  the 
division  of  labor  in  that  the  different  players  do  different 
things  —  one  catching,  another  pitching,  and  so  on.  A 
manufacturing  establishment  which  employs  several  work- 
men may  also  be  an  organization.  The  article  manufac- 
tured provides  the  common  purpose  toward  which  all  strive; 
and,  in  the  assignment  of  different  kinds  of  work  to  the 
individual  workmen,  the  principle  of  division  of  labor  is 
carried  out.  For  the  same  reason  a  school,  a  railway 
system,  an  army,  and  a  political  party  are  organizations. 

An  organization  of  a  lower  order  of  individuals  than 
these  human  organizations  is  to  be  found  in  a  hive  of  bees. 
This  is  made  up  of  the  individual  bees,  and  these,  in  carry- 
ing on  the  general  work  of  the  hive,  are  known  to  practice 
the  division  of  labor. 

Is  the  Body  an  Organization  ?  —  If  the  body  is  an  organ- 
ization, it  must  fulfill  the  conditions  of  the  definition.  It 


GENERAL   VIEW   OF   THE   BODY  n 

must  be  made  up  of  separate  or  individual  parts.  These 
must  work  together  for  the  same  general  purpose,  and,  in 
the  accomplishment  of  this  purpose,  must  practice  the  di- 
vision of  labor.  That  the  body  practices  the  division  of 
labor  is  seen  in  the  related  work  of  the  different  organs. 
That  it  is  made  up  of  minute,  but  individual,  parts  will  be 
shown  in  the  chapter  following.  That  it  carries  on  a  gen- 
eral work  which  is  accomplished  through  the  combined 
action  of  its  individual  parts  is  revealed  through  an  ex- 
tended study  of  its  various  activities.  The  body  is  an  or- 
ganization. Moreover,  it  is  one  of  the  most  complex  and, 
at  the  same  time,  most  perfect  of  the  organizations  of 
which  we  have  knowledge. 

Summary.  —  Viewed  from  the  outside,  the  body  is  seen 
to  be  made  up  of  divisions  which  are  more  or  less  familiar. 
Viewed  internally,  it  is  found  to  consist  of  different  kinds 
of  materials,  called  tissues.  The  tissues  are  adapted,  by 
their  properties,  to  different  purposes  both  in  the  con- 
struction of  the  body  and  in  carrying  on  its  work.  The 
working  parts  of  the  body  are  called  organs  and  these  in 
their  work  combine  to  form  systems.  The  entire  body,  on 
account  of  the  method  of  its  construction  and  the  character 
of  its  work,  may  be  classed  as  an  organization. 

Exercises.  —  i.  Name  and  locate  the  chief  external  divisions  of  the 
body. 

2.  What    tissues    may    be    found    by    dissecting    the    leg    of    a 
chicken  ? 

3.  Name  the  most  important  properties  and  the  most  important  uses 
of  muscular  tissue,  osseous  tissue,  and  connective  tissue. 

4.  Define  an  organ.     Define  a  system.     Name  examples  of  each. 

5.  Name  the  chief  cavities  of  the  body  and  the  organs  which  they 
contain. 

6.  What  tissues  are  present  in  the  hand  ?     How  does  each  of  these 
aid  in  the  work  of  the  hand  ? 


I2  THE   VITAL    PROCESSES 

7.  Define  an  organization.     Show  that  a  railway  system,  an  army, 
and  a  school  are  organizations. 

8.  What  is  meant  by  the  phrase   "division  of  labor"  ?     In  what 
manner  is  the  division  of  labor  practiced  in  a  shoe  or  watch  factory  ? 
What  are  the  advantages  ? 

9.  What  are  the  proofs  that  the  body  is  an  organization  ? 

PRACTICAL  WORK 

Observation  on  the  Tissues.  —  Examine  with  care  the  structures  in  the 
entire  leg  of  a  chicken,  squirrel, 'rabbit,  or  other  small  animal  used  for 
food.  Observe,  first  of  all,  the  external  covering,  consisting  of  cuticle 
and  hair,  claws,  scales,  or  feathers,  according  to  the  specimen.  These 
are  similar  in  structure,  and  they  form  the  epidermis,  which  is  one  kind 
of  epithelial  tissue.  With  a  sharp  knife  lay  open  the  skin  and  observe 
that  it  is  attached  to  the  parts  underneath  by  thin,  but  tough,  threads 
and  sheaths.  These  represent  a  variety  of  connective  tissue.  The  red- 
dish material  which  forms  the  greater  portion  of  the  specimen  is  a  va- 
riety of  muscular  tissue,  and  its  divisions  are  called  muscles.  With  a 
blunt  instrument,  separate  the  muscles,  by  tearing  apart  the  connective 
tissue  binding  them  together,  and  find  the  glistening  white  strips  of 
connective  tissue  (tendons)  which  attach  them  to  the  bones.  Find 
near  the  central  part  of  the  leg  a  soft,  white  cord  (a  nerve)  which  rep- 
resents one  variety  of  nervous  tissue.  The  bones,  which  may  now  be 
examined,  form  the  osseous  tissue.  At  the  ends  of  the  bones  will  be 
found  a  layer  of  smooth,  white  material  which  represents  one  kind  of 
cartilaginous  tissue.  The  adipose,  or  fatty,  tissue,  which  is  found  under 
the  skin  and  between  the  other  tissues,  is  easily  recognized. 

Relation  of  the  Tissues  to  the  Organs.  —  Observe  in  the  specimen 
just  studied  the  relation  of  the  different  tissues  to  the  organ  as  a  whole 
(regarding  the  leg  as  an  organ),  i.e.,  show  how  each  of  the  tissues 
aids  in  the  work  which  the  organ  accomplishes.  Show  in  particular 
how  the  muscles  supply  the  foot  with  motion,  by  tracing  out  the  ten- 
dons that  connect  them  with  the  toes.  Pull  on  the  different  tendons, 
noting  the  effect  upon  the  different  parts  of  the  foot. 


CHAPTER   III 
THE  BODY  ORGANIZATION 

WHAT  is  the  nature  of  the  body  organization  ?  What  are 
the  individual  parts,  or  units,  that  make  it  up  ?  What 
general  work  do  these  carry  on  and  upon  what  basis  do 
they  practice  the  division  of  labor  ?  The  answers  to  these 
questions  will  suggest  the  main  problems  in  the  study  of 
the  body. 

Complex  Nature  of  the  Tissues.  —  To  the  unaided  eye 
the  tissues  have  the  appearance  of  simple  structures.  The 
microscope,  however,  shows  just  the 
reverse  to  be  true.  When  any  one  of 
the  tissues  is  suitably  prepared  and 
carefully  examined  with  this  instru- 
ment, at  least  two  classes  of  materials 
can  be  made  out.  One  of  these  con- 
sists of  minute  particles,  called  cells ; 
the  other  is  a  substance  lying  between 
the  cells,  known  as  the  intercellular 
material  (Fig.  3).  The  cells  and  the 
intercellular  material,  though  varying  in  their  relative  pro- 
portions, are  present  in  all  the  tissues. 

The  Body  a  Cell  Group.  — The  biologist  has  found  that 
the  bodies  of  all  living  things,  plants  as  well  as  animals, 
consist  either  of  single  cells  or  of  groups  of  cells.  The 
single  cells  live  independently  of  one  another,  but  the  cells 
that  form  groups  are  attached  to,  and  are  more  or  less 
dependent  upon,  one  another.  In  the  first  condition  are 

13 


FIG.  3.  —  Diagram 
showing  the  relation  of 
the  cells  and  the  inter- 
cellular material.  C. 
Cells.  /.  Intercellular 
material. 


I4  THE  VITAL  PROCESSES 

found  the  very  lowest  forms  of  life.  In  the  second,  life 
reaches  its  greatest  development.  The  body  of  man, 
which  represents  the  highest  type  of  life,  is  recognized  as 
a  group  of  cells.  In  this  group  each  cell  is  usually  sepa- 
rate and  distinct  from  the  others,  but  is  attached  to  them, 
and  is  held  in  place  by  the  intercellular  material. 

Protoplasm,  the  Cell  Substance.  —  The  cell  is  properly 
regarded  as  an  organised  bit  of  a  peculiar  material,  called 
protoplasm.  This  is  a  semi-liquid  and  somewhat  granular 
substance  which  resembles  in  appearance  the  white  of  a 
raw  egg.  Its  true  nature  and  composition  are  unknown, 
because  any  attempt  to  analyze  it  kills  it,  and  dead  proto- 
plasm is  essentially  different  from  living  protoplasm.  It 
is  known,  however,  to  be  a  highly  complex  substance 
and  to  undergo  chemical  change  readily.  It  appears 
to  be  the  only  kind  of  matter  with  which  life  is  ever 
associated,  and  for  this  reason  protoplasm  is  called  the 
physical  basis  of  life.  Its  organization  into  separate 
bits,  or  cells,  is  necessary  to  the  life  activities  that  take 
place  within  it. 

Structure  of  the  Cell.  —  Though  all  portions  of  the  cell  are 
formed  from  the  protoplasm,  this  essential  substance  dif- 
fers both  in  structure  and  in  function  at  different  places  in 
the  cell.  For  this  reason  the  cell  is  looked  upon  as  a 
complex  body  having  several  distinct  parts.  At  or  near 
the  center  is  a  clear,  rounded  body,  called  the  nucleus. 
This  plays  some  part  in  the  nourishment  of  the  cell  and 
also  in  the  formation  of  new  cells.  If  it  be  absent,  as  is 
sometimes  the  case,  the  cell  is  short-lived  and  unable  to 
reproduce  itself.  The  variety  of  protoplasm  contained  in 
the  nucleus  is  called  the  nncleoplasm. 

Surrounding  the  nucleus  is  the  main  body  of  the  cell, 
sometimes  referred  to  as  the  "protoplasm."  Since  the 


THE   BODY   ORGANIZATION 


3 


protoplasm  forms  all  parts  of  the  cell,  this  substance  is 
more  properly  called  the  cytoplasm,  or  cell  plasm.  Sur- 
rounding and  inclosing  the  cytoplasm,  in  many  cells,  is  a 
thin  outer  layer,  or  membrane,  which  affords  more  or  less 
protection  to  the  contents  of  the  cell.  This  is  usually 
referred  to  as  the 
cell-wall.  A  fourth 
part  of  the  cell  is 
also  described,  being 
called  the  attraction 
sphere.  This  is  a 
small  body  lying 

near     the     nucleus 

j           ••             .  •  t^M-CsJKl^i.^xXrj;^-*-- 

and    cooperating  \^|iw®§^(9S 

with   that    body    in  5 — -K^raKr^ifcS^Xli 

the  formation  of 
new  cells.  Food  par- 
ticles, wastes,  and 
other  substances  w,FlG\ 4" ~ ^/P"11  ,of  a  tyPicf  cel1  (after 

Wilson).      I.  Mam  body.      2.  Nucleus.      3.  At- 

may  also  be  present  traction  sphere.  4.  Food  particles  and  waste, 
in  the  Cytoplasm.  5-  Cell-wall.  6.  Masses  of  active  material  found 
T-,I  r  .  in  certain  cells,  called  plastids. 

1  he  parts  of  a  typi- 
cal cell  are  shown  in  Fig.  4. 

Importance  of  the  Cells. — The  cells  must  be  regarded 
as  the  living,  working  parts  of  the  body.  They  are  the 
active  agents  in  all  of  the  tissues,  enabling  them  to  serve 
their  various  purposes.  Working  through  the  tissues,  they 
build  up  the  body  and  carry  on  its  different  activities. 
They  are  recognized  on  this  account  as  the  units  of  struc- 
ture and  of  function,  and  are  the  "individuals"  in  the 
body  organization.  Among  the  most  important  and  inter- 
esting of  the  activities  of  the  cells  are  those  by  which  they 
build  up  the  body,  or  cause  it  to  grow. 


i6 


THE   VITAL  PROCESSES 


How  the  Cells  enable  the  Body  to  Grow.  —  Every  cell  is 
able  to  take  new  material  into  itself  and  to  add  this  to  the 
protoplasm.  This  tends  to  increase  the  amount  of  the 
protoplasm,  thereby  causing  the  cells  to  increase  in  size. 
A  general  increase  in  the  size  of  the  cells  has  the  effect  of 
increasing  the  size  of  the  entire  body,  and  this  is  one  way 
by  which  they  cause  it  to  grow.  There  is,  however,  a 
fixed  limit,  varying  with  different  cells,  to  the  size  which 
they  attain,  and  this  is  quite  low.  (The  largest  cells  are 
scarcely  visible  to  the  naked  eye.)  Any  marked  increase 
in  the  size  of  the  body  must,  therefore,  be  brought  about 
by  other  means.  Such  a  means  is  found  in  the  formation 
of  new  cells,  or  cell  reproduction.  The  new  cells  are  al- 
ways formed  by  and  from  the  old  cells,  the  essential  process 
being  known  as  cell-division. 

Cell-Division.  —  By  dividing,  a  single  cell  will,  on  attain- 
ing its  growth,  separate  into  two  or  more  new  cells.  The 


FIG.  5.  —  Steps  in  cell-division  (after  Wilson).  Note  that  the  process 
begins  with  the  division  of  the  attraction  sphere,  then  involves  the  nucleus, 
and  finally  separates  the  main  body. 

process  is  quite  complex  and  is  imperfectly  understood. 
It  is  known,  however,  that  the  act  of  separation  is  pre- 
ceded by  a  series  of  changes  in  which  the  attraction  sphere 


THE    BODY   ORGANIZATION 


and  the  nucleus  actively  participate,  and  that,  as  a  result 
of  these  changes,  the  contents  of  the  old  cell  are  rear- 
ranged to  form  the  new  cells.  Some  of  the  different 
stages  in  the  process,  as  they  have  been  studied  under  the 
microscope,  are  indicated  in  Fig.  5. 

Gradually,  through  the  formation  of  new  cells  and  by 
the  growth  of  these  cells  after  they  have  been  formed,  the 
body  attains  its  full  size.  When  growth  is  complete,  cell 
reproduction  is  supposed  to  cease  except  where  the  tissues 
are  injured,  as  in  the  breaking  of  a  bone,  or  where  cells, 
like  those  at  the  surface  of  the  skin,  are  subject  to  wear. 
Then  new  material  continues  to  be  added 
to  the  protoplasm  throughout  life,  but 
in  amount  only  sufficient  to  replace  that 
lost  from  the  protoplasm  as  waste. 

Cell  Surroundings.  —  All  cells  are  said 
to  be  aquatic.  This  means  simply  that 
they  require  water  for  carrying  on  their 
various  activities.  The  cells,  in  order 
to  live,  must  take  in  and  give  out 
materials,  and  water  is  necessary  to 
both  processes.  It  is  also  an  essential 
part  of  the  protoplasm.  Deprived  of 
water,  cells  become  inactive  and  usually 
die.  Aquatic  surroundings  are  provided 
for  the  cells  of  the  body  through  a  liquid 
known  as  the  lymph,  which  is  distributed 
throughout  the  intercellular  material  (Fig.  6).  This  con- 
sists of  water  containing  oxygen  and  food  substances  in 
solution.  Besides  supplying  these  to  the  cells,  the  lymph 
also  receives  their  wastes.  Through  the  lymph  the  neces- 
sary conditions  for  cell  life  are  provided  in  the  body. 

The  General  Work  of  Cells.  —  In  handling  the  materials 


FIG.  6.  —  A  tum- 
bler partly  filled  with 
marbles  covered  with 
water,  suggesting  the 
relations  of  the  cells 
to  the  lymph. 


lg  THE   VITAL   PROCESSES 

derived  from  the  lymph,  the  cells  carry  on  three  well- 
defined  processes,  known  as  absorption,  assimilation,  and 
excretion. 

Absorption  is  the  process  of  taking  water,  food,  and 
oxygen  into  the  cells. 

Assimilation  is  a  complex  process  which  results  in  the 
addition  of  the  absorbed  materials  to  the  protoplasm. 
Through  assimilation  the  protoplasm  is  built  up  or  renewed. 

Excretion  is  the  throwing  off  of  such  waste  materials  as 
have  been  formed  in  the  cells.  These  are  passed  into  the 
lymph  and  thence  to  the  surface  of  the  body. 

Absorption,  assimilation,  excretion,  and  also  reproduc- 
tion are  performed  by  all  classes  of  cells.  They  are,  on 
this  account,  referred  to  as  the  general  work  of  cells. 

The  Special  Work  of  Cells.  —  In  addition  to  the  general 
work  which  all  cells  do  in  common,  each  class  of  cells  in 
the  body  is  able  to  do  some  particular  kind  of  work  —  a 
work  which  the  others  cannot  do  or  which  they  can  do 
only  to  a  limited  extent.  This  is  spoken  of  as  the  special 
work  of  cells.  Examples  of  the  special  work  of  cells  are 
found  in  the  production  of  motion  by  muscle  cells  and  in 
the  secretion  of  liquids  by  gland  cells.  It  may  be  noted 
that  while  the  general  work  of  cells  benefits  them  individ- 
ually, their  special  work  benefits  the  body  as  a  whole. 
Another  example  of  the  special  work  of  cells  is  found  in 
the 

Production  of  the  Intercellular  Material.  —  Though  most 
of  the  cells  of  the  body  deposit  to  a  slight  extent  this 
material,  the  greater  part  of  it  is  produced  by  a  single  class 
of  cells  found  in  bone,  cartilage,  and  connective  tissue. 
Cartilage,  bone,  and  connective  tissue  differ  greatly  from 
the  other  tissues  in  the  amount  of  intercellular  material 
which  they  contain,  the  difference  being  due  to  these  cells. 


THE    BODY   ORGANIZATION  19 

In  the  connective  tissue  they  deposit  the  fibrous  material 
so  important  in  holding  the  different  parts  of  the  body 
together.  In  the  cartilage  they 
produce  the  gristly  substance  which 
forms  by  far  its  larger  portion 
(Fig.  7).  In  the  bones  they  de- 
posit a  material  similar  to  that  in 
the  cartilage,  except  that  with  it 
is  mixed  a  mineral  substance  which 

gives     the    bones    their     hardness 

,       ,_,        .  FIG.  7. — Cartilage  cells, 

and    stiffness.1      The    intercellular   surrounded  by  the  intercel- 


material,  in  addition  to  connecting   lular  material  which  they 
the  cells,  supplies  to  certain  tissues    have  deP°sited- 
important  properties,   such  as  the  elasticity  of  cartilage 
and  the  stiffness  of  the  bones. 

Nature  of  the  Body  Organization.  —  The  division  of  labor 
carried  on  by  the  different  organs,  as  shown  in  the  pre- 
ceding chapter,  is  in  reality  carried  on  by  the  cells  that 
form  the  organs.  To  see  that  this  is  true  we  have  only  to 
observe  the  relation  of  cells  to  tissues  and  of  tissues  to 
organs.  The  cells  form  the  tissues  and  the  tissues  form 
the  organs.  This  arrangement  enables  the  special  work 
of  different  kinds  of  cells  to  be  combined  in  the  work  of 
the  organ  as  a  whole.  This  is  seen  in  the  hand  which,  in 
grasping,  uses  motion  supplied  by  the  muscle  cells,  a  con- 
trolling influence  supplied  by  the  nerve  cells,  a  framework 
supplied  by  the  bone  cells,  and  so  on.  The  cells  supply 
the  basis  for  the  body  organization  and,  properly  speaking, 
the  body  is  an  organisation  of  cells?  (Recall  the  definition 

1  Certain  of  these  cells  also  form  deposits  of  fat,  giving  rise  to  the  adipose,  or 
fatty,  tissue. 

2  Any  organized  structure,  such  as  the  body,  whose  parts  are  pervaded  by  a 
common  life,  is  known  as  an  organism.    The  term  "organism"  is  frequently  ap- 
plied to  the  body. 


20  THE   VITAL   PROCESSES 

of  an  organization,  page  10.)     In  this  organization  there 
are  to  be  observed  : 

1.  A  definite  arrangement  of  the  cells  to  form  the  tis- 
sues.    A  tissue  is  a  group  of  like  cells. 

2.  A  definite  arrangement  of  the  tissues  in  the  organ. 
Each  organ  contains  the  tissues  needed  for  its  work. 

3.  In  several  instances  there  is  a  definite  arrangement 
of  organs  to  form  systems. 

4.  The  body  as  a  whole  is  made  up  of  organs  and  sys- 
tems, together  with  the  structures  necessary  for  their  sup- 
port and  protection. 

There  now  remains  a  further  question  for  considera- 
tion. What  is  the  one  supreme  end,  or  purpose,  toward 
which  all  the  activities  of  the  body  organization  are 
directed  ?  This  purpose  will  naturally  have  some  relation 
to  the  maintenance,  or  preservation,  of  the  cell  group 
which  we  call  the  body. 

The  Maintenance  of  Life.  —  The  preservation  of  any  cell 
group  in  its  natural  condition,  whether  it  be  plant  or  animal, 
is  accomplished  through  keeping  it  alive.  If  life  ceases, 
the  group  quickly  disintegrates  and  its  elements  become 
scattered,  a  fact  which  is  verified  through  everyday  ob- 
servation. Though  the  nature  of  life  is  unknown,  it  may 
be  looked  upon  as  the  organizer  and  preserver  of  the 
protoplasm.  But  in  preserving  the  protoplasm  it  also 
preserves  the  entire  cell  group,  or  body.  Life  is  thus 
the  most  essential  condition  of  the  body.  With  life  all 
portions  of  the  body  are  concerned,  and  toward  its  mainte- 
nance all  the  activities  of  the  body  organisation  are  directed. 

The  Nutrient  Fluid  in  its  Relations  to  the  Cells.  —  The 
maintenance  of  life  within  the  cells  requires,  as  we  have 
seen,  that  they  be  supplied  with  water,  food,  and  oxygen, 
and  that  they  be  relieved  of  such  wastes  as  they  form. 


THE    BODY    ORGANIZATION  21 

This  double  purpose  is  accomplished  through  the  agency 
of  an  internal  nutrient  fluid,  a  portion  of  which  has  already 
been  referred  to  as  the  lymph.  Not  only  does  this  fluid 
supply  the  means  for  keeping  the  cells  alive,  but,  through 
the  cells,  it  is  also  the  means  of  preserving  the  life  of  the 
body  as  a  whole. 

The  cells,  however,  rapidly  exhaust  the  nutrient  .fluid. 
They  take  from  it  food  and  oxygen  and  they  put  into  it 
their  wastes.  To  prevent  its  becoming  unfit  for  supplying 
their  needs,  food  and  oxygen  must  be  continually  added 
to  this  fluid,  and  waste  materials  must  be  continually  re- 
moved. This  is  not  an  easy  task.  As  a  matter  of  fact, 
the  preparation,  distribution,  and  purification  of  the  nutrient 
fluid  requires  the  direct  or  indirect  aid  of  practically  all 
parts  of  the  body.  It  supplies  for  this  reason  a  broad 
basis  for  the  division  of  labor  on  the  part  of  the  cells. 

Relation  of  the  Body  to  its  Environment.  —  While  life 
is  directly  dependent  upon  the  internal  nutrient  fluid,  it  is 
indirectly  dependent  upon  the  physical  surroundings  of  the 
body.  Herein  lies  the  need  of  the  external  organs  —  the 
feet  and  legs  for  moving  about,  the  hands  for  handling 
things,  the  eyes  for  directing  movements,  etc.  That  the 
great  needs  of  the  body  are  supplied  from  its  surroundings 
are  facts  of  common  experience.  Food,  shelter,  air,  cloth- 
ing, water,  and  the  means  of  protection  are  external  to  the 
body  and  form  a  part  of  its  environment.  In  making  the 
things  about  him  contribute  to  his  needs,  man  encounters 
a  problem  which  taxes  all  his  powers.  Only  by  toil  and 
hardship,  "  by  the  sweat  of  his  brow,"  has  he  been  able  to 
wrest  from  his  surroundings  the  means  of  his  sustenance. 

The  Main  Physiological  Problems. — The  study  of  the 
body  is  thus  seen  to  resolve  itself  naturally  into  the  con- 
sideration of  two  main  problems  ; 


22  THE   VITAL   PROCESSES 

1.  That  of  maintaining  in  the  body  a  nutrient  fluid  for 

the  cells. 

2.  That  of  bringing  the  body  into  such  relations  with  its 
surroundings  as  will  enable  it  to  secure  materials  for  the 
nutrient  fluid  and  satisfy  its  other  needs. 

The  first  problem  is  internal  and  includes  the  so-called 
vital  processes,  known  as  digestion,  circulation,  respiration, 
and  excretion.  The  second  problem  is  external,  as  it  were, 
and  includes  the  work  of  the  external  organs  —  the  organs 
of  motion  and  of  locomotion  and  the  organs  of  special 
sense.  These  problems  are  closely  related,  since  they  are 
the  two  divisions  of  the  one  problem  of  maintaining  life. 
Neither  can  be  considered  independently  of  the  other.  In 
the  chapter  following  is  taken  up  the  first  of  these  problems. 

Summary.  — The  individual  parts,  or  units,  that  form  the 
body  organization  are  known  as  cells.  These  consist  of 
minute  but  definitely  arranged  portions  of  protoplasm  and 
are  held  together  by  the  intercellular  material.  They  build 
up  the  body  and  carry  on  its  different  activities.  The 
tissues  are  groups  of  like  cells.  By  certain  general  activ- 
ities the  cells  maintain  their  existence  in  the  tissues  and  by 
the  exercise  of  certain  special  activities  they  adapt  the 
tissues  to  their  purposes  in  the  body.  The  body,  as  a  cell 
organization,  has  its  activities  directed  under  normal  con- 
ditions toward  a  single  purpose  —  that  of  maintaining  life. 
In  the  accomplishment  of  this  purpose  a  nutrient  fluid  is 
provided  for  the  cells  and  proper  relations  between  the 
body  and  its  surroundings  are  established. 

Exercises.  —  i.  If  a  tissue  be  compared  to  a  brick  wall,  to  what  do 
the  separate  bricks  correspond  ?  To  what  the  mortar  between  the  bricks  ? 

2.  Draw  an  outline  of  a  typical  cell,  locating  and  naming  the  main 
divisions. 

3.  How  do  the  cells  enable  the  body  to  grow  ?     Describe  the  process 
of  cell-division. 


THE    BODY   ORGANIZATION  23 

4.  How  does  the  general  work   of  cells    differ   from    their  special 
work  ?      Define   absorption,  excretion,  and  assimilation  as  applied  to 
the  cells. 

5.  Compare  the  conditions  surrounding  a  one-celled  animal,  living 
in  water,  to  the  conditions  surrounding  the  cells  in  the  body. 

6.  What  is  meant  by  the  term  "environment"  ?     How  does  man's 
environment  differ  from  that  of  a  fish  ? 

7.  What  is  the  necessity  for  a  nutrient  fluid  in  the  body  ? 

8.  Why  is  the  maintenance  of  life  necessarily  the  chief  aim  of  all 
the  activities  of  the  boay  ? 

9.  State  the  twp^main  problems  in  the  study  of  the  body. 

PRACTICAL   WORK 

Observations.  —  i.  Make  some  scrapings  from  the  inside  of  the 
cheek  with  a  dull  knife  and  mix  these  with  a  little  water  on  a  glass 
slide.  Place  a  cover-glass  on  the  same  and  examine  with  a  compound 
microscope.  The  large  pale  cells  that  can  be  seen  in  this  way  are 
a  variety  of  epithelial  cells. 

2.  Mount  in  water  on  a  glass  slide  some  thin  slices  of  cartilage  and 
examine  first  with  a  low  and  then  with  a  high  power  of  microscope. 
(Suitable  slices  may  be  cut,  with  a  sharp  razor,  from  the  cartilage  found 
at  the  end  of  the  rib  of  a  young  animal.)     Note  the  small  groups  of 
cells  surrounded  by,  and  imbedded  in,  the  intercellular  material. 

3.  Mount  and  examine  with  the  microscope  thin  slices  of  elder  pith, 
potato,  and  the  stems  of  growing  plants.     Make  drawings  of  the  cells 
thus  observed. 

4.  Examine  with  the  microscope  a  small  piece  of  the  freshly  sloughed 
off  epidermis  of  a  frog's  skin.     Examine  it  first  in  its  natural  condition, 
and  then  after  soaking  for  an  hour  or  two  in  a  solution  of  carmine. 
Make  drawings. 

5.  Mount  on  a  glass  slide  some  of  the  scum  found  on  stagnant  water 
and  examine  it  with  a  compound  microscope.     Note  the  variety  and 
relative  size  of  the  different  things  moving  about.     The  forms  most 
frequently  seen  by  such  an  examination  are  one-celled  plants.     Many 
of  these  have  the  power  of  motion. 

6.  Examine  tissues  of  the  body,  such  as  nervous,  muscular,  and  glan- 
dular tissues,  which  have  been  suitably  prepared  and  mounted  for  micro- 
scopic study,  using  low  and  high  powers  of  the  microscope.      Make 
drawings  of  the  cells  in  the  different  tissues  thus  observed. 


CHAPTER   IV 
THE  BLOOD 

Two  liquids  of  similar  nature  are  found  in  the  body, 
known  as  the  blood  and  the  lymph.  These  are  closely 
related  in  function  and  together  they  form  the  nutrient 
fluid  referred  to  in  the  preceding  chapter.  The  blood  is 
the  more  familiar  of  the  two  liquids,  and  the  one  which 
can  best  be  considered  at  this  time. 

The  Blood  :  where  Found.  —  The  blood  occupies  and 
moves  through  a  system  of  closed  tubes,  known  as  the 
blood  vessels.  By  means  of  these  vessels  the  blood  is 
made  to  circulate  through  all  parts  of  the  body,  but  from 
them  it  does  not  escape  under  normal  conditions.  Though 
provisions  exist  whereby  liquid  materials  may  both  enter 
and  leave  the  blood  stream,  it  is  only  when  the  blood 
vessels  are  cut  or  broken  that  the  blood,  as  blood,  is  able 
to  escape  from  its  inclosures. 

Physical  Properties  of  the  Blood.  —  Experiments  such  as 
those  described  at  the  close  of  this  chapter  reveal  the 
more  important  physical  properties  of  the  blood.  It  may 
be  shown  to  be  heavier  and  denser  than  water ;  to  have 
a  faint  odor  and  a  slightly  salty  taste ;  to  have  a  bright 
red  color  when  it  contains  oxygen  and  a  dark  red  color 
when  oxygen  is  absent;  and  to  undergo,  when  exposed 
to  certain  conditions,  a  change  called  coagulation.  These 
properties  are  all  accounted  for  through  the  different 
materials  that  enter  into  the  formation  of  the  blood. 

24 


THE   BLOOD  25 

Composition  of  the  Blood.  —  To  the  naked  eye  the  blood 
appears  as  a  thick  but  simple  liquid  ;  but  when  examined 
with  a  compound  microscope,  it  is  seen  to  be  complex  in 
nature,  consisting  of  at  least  two  distinct  portions.  One  of 
these  is  a  clear,  transparent  liquid  ;  while  the  other  is  made 
up  of  many  small,  round  bodies  that  float  in  the  liquid. 
The  liquid  portion  of  the  blood  is  called  the  plasma  ;  the 
small  bodies  are  known  as  corpuscles.  Two  varieties  of 


Poo 


FIG.  8.  —  Blood  corpuscles,  highly  magnified.  A.  Red  corpuscles  as  they 
appear  in  diluted  blood.  B.  Arrangement  of  red  corpuscles  in  rows  between 
which  are  white  corpuscles,  as  may  be  seen  in  undiluted  blood.  C.  Red  cor- 
puscles much  enlarged  to  show  the  form. 

corpuscles  are  described  —  the  red  corpuscles  and  the 
white  corpuscles  (Fig.  8).  Other  round  particles,  smaller 
than  the  corpuscles,  may  also  be  seen  under  favorable 
conditions.  These  latter  are  known  as  blood  platelets. 

Red  Corpuscles.  —  The  red  corpuscles  are  classed  as 
cells,  although,  as  found  in  the  blood  of  man  and  the 
other  mammals  (Fig.  9),  they  have  no  nuclei.1  Each  one 
consists  of  a  little  mass  of  protoplasm,  called  the  stroma, 
which  contains  a  substance  having  a  red  color,  known 
as  hemoglobin.  The  shape  of  the  red  corpuscle  is  that 
of  a  circular  disk  with  concave  sides.  It  has  a  width  of 
about  of  an  mch  (7-9  microns2)  and  a  thickness  of 


1  In  birds,  reptiles,  amphibians,  and  fishes  the  red  corpuscles  have  nuclei  (Fig.  9). 

2  The  micron  is  the  unit  of  microscopical  measurements.     It  is  equal  to  uW  OJ 
a  millimeter  and  is  indicated  by  the  symbol  M. 


26  THE  VITAL   PROCESSES 


about  ^fotf  of  an  inch  (1.9  microns).  The  red  corpuscles 
are  exceedingly  numerous,  there  being  as  many  as  five 
millions  in  a  small  drop  (one  cubic  millimeter)  of  healthy 


FIG.  9.  —  Red  corpuscles  from  various  animals.  Those  from  mammals 
are  without  nuclei,  while  those  from  birds  and  cold-blooded  animals  have 
nuclei. 

blood.     But  the  number  varies  somewhat  and  is  greatly 
diminished  during  certain  forms  of  disease. 

It  is  the  function  of  the  red  corpuscles  to  serve  as 
oxygen  carriers  for  the  cells.  They  take  up  oxygen  at 
the  lungs  and  release  it  at  the  cells  in  the  different  tissues.1 
The  performance  of  this  function  depends  upon  the  hemo- 
globin. 

Hemoglobin.  —  This  substance  has  the  remarkable  property  of  form- 
ing, under  certain  conditions,  a  weak  chemical  union  with  oxygen  and, 
when  the  conditions  are  reversed,  of  separating  from  it.  It  forms 

1  The  peculiar  shape  of  the  red  corpuscle  has  no  doubt  some  relation  to  its 
work.  Its  circular  form  is  of  advantage  in  getting  through  the  small  blood  vessels, 
while  its  extreme  thinness  brings  all  of  its  contents  very  near  the  surface  —  a  con- 
dition which  aids  the  hemoglobin  in  taking  up  oxygen.  If  the  corpuscles  were 
spherical  in  shape,  some  of  the  hemoglobin  could  not,  on  account  of  the  distance 
from  the  surface,  so  readily  unite  with  the  oxygen. 


THE   BLOOD  27 

about  nine  tenths  of  the  solid  matter  of  the  red  corpuscles  and  to  it  is 
due  the  colors  of  the  blood.  When  united  with  the  oxygen  it  forms  a 
compound,  called  oxy 'hemoglobin,  which  has  a  bright  red  color;  the 
hemoglobin  alone  has  a  dark  red  color.  These  colors  are  the  same  as 
those  of  the  blood  as  it  takes  on  and  gives  off  oxygen.  The  stroma, 
which  forms  only  about  one  tenth  of  the  solid  matter  of  the  corpuscles, 
serves  as  a  contrivance  for  holding  the  hemoglobin.  The  conditions 
which  cause  the  hemoglobin  to  unite  with  oxygen  in  the  lungs  and  to 
separate  from  it  in  the  tissues,  will  be  considered  later  (Chapter  VIII). 

Disappearance  and  Origin  of  Red  Corpuscles.  —  The  red  corpuscles, 
being  cells  without  nuclei,  are  necessarily  short-lived.  It  has  been 
estimated  that  during  a  period  of  one  to  two  months,  all  the  red 
corpuscles  in  the  body  at  a  given  time  will  have  disappeared  and  their 
places  taken  by  new  ones.  The  origin  of  new  corpuscles,  however,  and 
the  manner  of  ridding  the  blood  of  old  ones  are  problems  that  are  not 
as  yet  fully  solved.  The  removal  of  the  products  of  broken  down 
corpuscles  is  supposed  to  take  place  both  in  the  liver  and  in  the  spleen.1 

Regarding  the  origin  of  the  red  corpuscles,  the  evidence  now  seems 
conclusive  that  large  numbers  of  them  are  formed  in  the  red  marrow  of 
the  bones.  The  red  marrow  is  located  in  what  is  known  as  the  spongy 
substance  of  the  bones  (Chapter  XIV)  and  consists,  to  a  large  extent, 
of  cells  somewhat  like  the  red  corpuscles,  but  differing  from  them  in 
having  nuclei.  These  appear  to  be  constantly  in  a  state  of  repro- 
duction. The  blood,  flowing  through  the  minute  cavities  containing 
these  cells,  carries  those  that  have  been  loosened  out  into  the  blood 
stream.  Nuclei  appear  in  the  red  corpuscles  at  the  time  of  their  forma- 
tion, but  these  quickly  separate  and,  according  to  some  authorities, 
form  the  blood  platelets. 

White  Corpuscles.  —  The  white  corpuscles,  or  leucocytes, 
are  cells  of  a  general  spherical  shape,  each  containing  one, 
two,  or  more  nuclei.  They  are  much  less  numerous  than 
the  red,  there  being  on  the  average  only  one  white  cor- 

1  The  coloring  matter  of  the  bile  consists  of  compounds  formed  by  the  breaking 
down  of  the  hemoglobin ;  the  spleen  contains  many  large  cells  that  seem  to 
have  the  power  first  of  "engulfing"  and  later  of  decomposing  red  corpuscles.  A 
further  evidence  that  the  spleen  aids  in  the  removal  of  worn-out  corpuscles  is 
found  in  the  fact  that  during  diseases  that  cause  a  destruction  of  the  red  corpuscles, 
such  as  the  different  forms  of  malaria,  the  spleen  becomes  enlarged. 


23  THE    VITAL   PROCESSES 

puscle  to  about  every  five  hundred  of  the  red  ones.  On 
the  other  hand,  the  white  corpuscles  are  larger  than  the 
red,  one  of  the  former  being  equal  in  volume  to  about 
three  of  the  latter. 

The  white  corpuscles  are  found,  when  studied  under 
favorable  conditions,  to  possess  the  power  of  changing 
their  shape  and,  by  this  means,  of  moving  from  place  to 


FIG.  10.  —  Escape  of  white  corpuscles  from  a  small  blood  vessel 
(Hall).  At  A  the  conditions  are  normal,  but  at  B  some  excitation  in  the 
surrounding  tissue  leads  to  a  migration  of  corpuscles.  I,  2,  and  3  show  differ- 
ent stages  of  the  passage. 

place.  This  property  enables  them  to  penetrate  the  walls 
of  capillaries  and  to  pass  with  the  lymph  in  between  the 
cells  of  the  tissues.  The  white  corpuscles  are,  therefore, 
not  confined  to  the  blood  vessels,  as  are  the  red  corpuscles, 
but  migrate  through  the  intercellular  spaces  (Fig.  10).  If 
any  part  of  the  body  becomes  inflamed,  the  white  corpus 
cles  collect  there  in  large  numbers ;  and,  on  breaking 
down,  they  form  most  of  the  white  portion  of  the  sore, 
called  the  pus. 


THE   BLOOD  59 

New  white  corpuscles  are  formed  from  old  ones,  by  cell-division. 
Their  production  may  occur  in  almost  any  part  of  the  body,  but  usually 
takes  place  in  the  lymphatic  glands  (Chapter  VI)  and  in  the  spleen, 
where  conditions  for  their  development  are  especially  favorable.  In 
these  places  they  are  found  in  great  abundance  and  in  various  stages  of 
development. 

Functions  of  White  Corpuscles.  —  The  main  use  of  the 
white  corpuscles  appears  to  be  that  of  a  destroyer  of 
disease  germs.  These  consist  of  minute  organisms  that 
find  their  way  into  the  body  and,  by  living  upon  the  tis- 
sues and  fluids  and  by  depositing  toxins  (poisons)  in  them, 
cause  different  forms  of  disease.  Besides  destroying  germs 
that  may  be  present  in  the  blood,  the  white  corpuscles  also 
leave  the  blood  and  attack  germs  that  have  invaded  the 
cells.  By  forming  a  kind  of  wall  around  any  foreign  sub- 
stance, such  as  a  splinter,  that  has  penetrated  the  skin, 
they  are  able  to  prevent  the  spread  of  germs  through  the 
body.  In  a  similar  manner  they  also  prevent  the  germs 
from  boils,  abscesses,  and  sore  places  in  general  from 
getting  to  and  infecting  other  parts  of  the  body.1  An- 
other function  ascribed  to  the  white  corpuscles  is  that  of 
aiding  in  the  coagulation  of  the  blood  (page  31);  and  still 
another,  of  aiding  in  the  healing  of  wounds. 

Plasma.  —  The  plasma  is  a  complex  liquid,  being  made 
up  of  water  and  of  substances  dissolved  in  the  water.  The 
dissolved  substances  consist  mainly  of  foods  for  the  cells 
and  wastes  from  the  cells. 

i.  The  foods  represent  the  same  classes  of  materials  as 
are  taken  in  the  daily  fare,  i.e.,  proteids,  carbohydrates, 

1  An  infected  part  of  the  body,  such  as  a  boil  or  abscess,  should  never  be  bruised 
or  squeezed  until  the  time  of  opening.  Pressure  tends  to  break  down  the  wall  of 
white  corpuscles  and  to  spread  the  infection.  Pus  from  a  sore  contains  germs 
and  should  not,  on  this  account,  come  in  contact  with  any  part  of  the  skin.  (See 
treatment  of  skin  wounds,  Chapter  XVI.) 


30  THE   VITAL   PROCESSES 

fats,  and  salts  (Chapter  IX).  Three  kinds  of  proteids 
are  found  in  the  plasma,  called  serum  albumin,  scrum 
globulin,  and  fibrinogen.  These  resemble,  in  a  general 
way,  the  white  of  raw  egg,  but  differ  from  each  other  in  the 
readiness  with  which  they  coagulate.  Fibrinogen  coagu- 
lates more  readily  than  the  others  and  is  the  only  one  that 
changes  in  the  ordinary  coagulation  of  the  blood.  The 
others  remain  dissolved  during  this  process,  but  are  coagu- 
lated by  chemical  agents  and  by  heat.  While  all  of  the 
proteids  probably  serve  as  food  for  the  cells,  the  fibrino- 
gen, in  addition,  is  a  necessary  factor  in  the  coagulation  of 
the  blood  (page  31). 

The  only  representative  of  the  carbohydrates  in  the 
plasma  is  dextrose.  This  is  a  variety  of  sugar,  being  de- 
rived from  starch  and  the  different  sugars  that  are  eaten. 
The  fat  in  the  plasma  is  in  minute  quantities  and  appears 
as  fine  droplets — the  form  in  which  it  is  found  in  milk. 
While  several  mineral  salts  are  present  in  small  quantities 
in  the  plasma,  sodium  chloride,  or  common  salt,  is  the 
only  one  found  in  any  considerable  amount.  The  mineral 
salts  serve  various  purposes,  one  of  which  is  to  cause  the 
proteids  to  dissolve  in  the  plasma. 

2.  The  wastes  are  formed  at  the  cells,  whence  they  are 
passed  by  the  lymph  into  the  blood  plasma.  They  are  car- 
ried by  the  blood  until  removed  by  the  organs  of  excretion. 
The  two  waste  products  found  in  greatest  abundance  in 
the  plasma  are  carbon  dioxide  and  urea. 

The  substances  dissolved  in  the  plasma  form  about  10 
per  cent  of  the  whole  amount.  The  remaining  90  per 
cent  is  water.  Practically  all  the  constituents  of  the 
plasma,  except  the  wastes,  enter  the  blood  from  the  digest- 
ive organs. 

Purposes  of  Water  in  the  Blood.  —  Not  only  is  water  the 


THE    BLOOD  31 

most  abundant  constituent  of  the  blood;  it  is,  in  some 
respects,  the  most  important.  It  is  the  liquefying  por- 
tion of  the  blood,  holding  in  solution  the  constituents  of 
the  plasma  and  floating  the  corpuscles.  Deprived  of  its 
water,  the  blood  becomes  a  solid  substance.  Through  the 
movements  of  the  blood  the  water  also  serves  the  purpose 
of  a  transporting  agent  in  the  body.  The  cells  in  all  parts 
of  the  body  require  water  and  this  is  supplied  to  them 
from  the  blood.  Water  is  present  in  the  corpuscles  as 
well  as  in  the  plasma  and  forms  about  80  per  cent  of  the 
entire  volume  of  the  blood. 

Coagulation  of  the  Blood.  —  If  the  blood  is  exposed  to 
some  unnatural  condition,  such  as  occurs  when  it  escapes 
from  the  blood  vessels,  it  undergoes  a  peculiar  change 
known  as  coagulation!  In  this  change  the  corpuscles  are 
collected  into  a  solid  mass,  known  as  the  clot,  thereby 
separating  from  a  liquid  called  the  serum.  The  serum, 
which  is  similar  in  appearance  to  the  blood  plasma,  differs 
from  that  liquid  in  one  important  respect  as  explained 
below. 

Causes  of  Coagulation.  —  Although  coagulation  affects  all 
parts  of  the  blood,  only  one  of  its  constituents  is  found  in 
reality  to  coagulate.  This  is  the  fibrinogen.  The  forma- 
tion of  the  clot  and  the  separation  of  the  serum  is  due 
almost  entirely  to  the  action  of  this  substance.  Fibrino- 
gen is  for  this  reason  called  the  coagnlable  constituent  of 
the  blood.  In  the  plasma  the  fibrinogen  is  in  a  liquid 
form ;  but  during  coagulation  it  changes  into  a  white, 
stringy  solid,  called  ^rz>/.  This  appears  in  the  clot  and  is 
the  cause  of  its  formation.  Forming  as  a  network  of  exceed- 

1  Coagulation  is  not  confined  to  the  blood.  The  white  of  an  egg  coagulates 
when  heated  and  when  acted  upon  by  certain  chemicals,  and  the  clabbering  o( 
milk  also  is  a  coagulation. 


THE   VITAL   PROCESSES 


ingly  fine  and  very  delicate  threads  (Fig.  \\}  throughout  the 
mass  of  blood  that  is  coagulating,  the  fibrin  first  entangles 

the  corpuscles  and  then,  by 
contracting,  draws  them  into 
the  solid  mass  or  clot.1  The 
contracting  of  the  fibrin  also 
squeezes  out  the  serum. 
This  liquid  contains  all  the 
constituents  of  the  plasma 
except  the  fibrinogen. 

FIG.  ii.  — Fibrin  threads  (after  Fibrin  Ferment  and  Calcium. — 
Ranvier).  These  by  contracting  draw  Most  difficult  of  all  to  answer  have 
the  corpuscles  together  and  form  the  been  the  questions  :  What  causes 
c'ot<  the  blood  to  coagulate  outside  of  the 

blood  vessels  and  what  prevents  its  coagulation  inside  of  these  vessels  ? 
The  best  explanation  offered  as  yet  upon  this  point  is  as  follows : 
Fibrinogen  does  not  of  itself  change  into  fibrin,  but  is  made  to  undergo 
this  change  by  the  presence  of  another  substance,  calledy&Ww  ferment. 
This  substance  is  not  a  regular  constituent  of  the  blood,  but  is  formed 
as  occasion  requires.  It  is  supposed  to  result  from  the  breaking  down 
of  the  white  corpuscles,  and  perhaps  also  from  the  blood  platelets,  when 
the  blood  is  exposed  to  unnatural  conditions.  The  formation  of  the 
ferment  leads  in  turn  to  the  changing  of  the  fibrinogen  into  fibrin. 

Another  substance  which  is  necessary  to  the  process  of  coagula- 
tion is  the  element  calcium.  If  compounds  of  calcium  are  absent  from 
the  blood,  coagulation  does  not  take  place.  These  are,  however, 
regular  constituents  of  healthy  blood.  Whether  the  presence  of  the 
calcium  is  necessary  to  the  formation  of  the  ferment  or  to  the  action 
of  the  ferment  upon  the  fibrinogen  is  unknown. 

Purpose  of  Coagulation.  —  The  purpose  of  coagulation 
is  to  check  the  flow  of  blood  from  wounds.  The  fact  that 
the  blood  is  contained  in  and  kept  flowing  continuously 

1  If  the  blood  be  stirred  or  "whipped"  while  it  is  coagulating,  the  clot  may  be 
broken  up  and  the  fibrin  separated  as  fast  as  it  forms.  The  blood  which  then 
remains  consists  of  serum  and  corpuscles  and  will  not  coagulate.  It  is  known  as 
"  defibrinated  "  blood. 


THE   BLOOD  33 

through  a  system  of  connected  vessels  causes  it  to  escape 
rapidly  from  the  body  whenever  openings  in  these  vessels 
are  made.  Clots  form  at  such  openings  and  close  them  up, 
stopping  in  this  way  the  flow  that  would  otherwise  go  on 
indefinitely.  Coagulation,  however,  does  not  stop  the  flow 
of  blood  from  the  large  vessels.  From  these  the  blood  runs 
with  too  great  force  for  the  clot  to  form  within  the  wound. 

Time  Required  for  Coagulation.  —  The  rate  at  which  coagulation 
takes  place  varies  greatly  under  different  conditions.  It  is  influenced 
strongly  by  temperature;  heat  hastens  and  cold  retards  the  process. 
It  may  be  prevented  entirely  by  lowering  the  temperature  of  the 
blood  to  near  the  freezing  point.  The  presence  of  a  foreign  substance 
increases  the  rapidity  of  coagulation,  and  it  has  been  observed  that 
bleeding  from  small  wounds  is  more  quickly  checked  by  covering  them 
with  linen  or  cotton  fibers.  The  fibers  in  this  case  hasten  the  process 
of  coagulation. 

Quantity  of  Blood.  —  The  quantity  of  blood  is  estimated  to  be 
about  one  thirteenth  of  the  entire  weight  of  the  body.  "This  for  the 
average  individual  is  an  amount  weighing  nearly  twelve  pounds  and 
having  a  volume  of  nearly  one  and  one  half  gallons.  About  46  per  cent 
by  volume  of  this  amount  is  made  up  of  corpuscles  and  54  per  cent  of 
plasma.  Of  the  plasma  about  10  per  cent  consists  of  solids  and  90 
per  cent  of  water,  as  already  stated. 

Functions  of  the  Blood.  —  The  blood  is  the  great  carry- 
ing, or  distributing,  agent  in  the  body.  Through  its  move- 
ments (considered  in  the  next  chapter)  it  carries  food  and 
oxygen  to  the  cells  and  waste  materials  from  the  cells. 
Much  of  the  blood  may,  therefore,  be  regarded  as  freight 
in. the  process  of  transportation.  The  blood  also  carries, 
or  distributes,  heat.  Taking  up  heat  in  the  warm  parts  of 
the  body,  it  gives  it  off  at  places  having  a  lower  tempera- 
ture. This  enables  all  parts  of  the  body  to  keep  at  about 
the  same  temperature. 

In  addition  to  serving  as  a  carrier,  the  blood  has  anti- 
septic properties,  i.e.,  it  destroys  disease  germs.  While 


34 


THE    VITAL   PROCESSES 


this  function  is  mainly  due  to  the  white  corpuscles,  it  is 
due  in  part  to  the  plasma.1  Through  its  coagulation,  the 
blood  also  closes  leaks  in  the  small  blood  vessels.  The 
blood  is  thus  seen  to  be  a  liquid  of  several  functions. 

Changes  in  the  Blood.  —  In  performing  its  functions  in 
the  body  the  blood  must  of  necessity  undergo  rapid  and 
continuous  change.  The  red  corpuscles,  whose  changes 
have  already  been  noted,  appear  to  be  the  most  enduring 
constituents  of  the  blood.  The  plasma  is  the  portion  that 
changes  most  rapidly.  Yet  in  spite  of  these  changes  the 

quantity  and  character  of 
the  blood  remain  prac- 
tically constant.2  This  is 
because  there  is  a  balan- 
cing of  the  forces  that 
FIG.  12.  — A  balanced  change  in  water.  ... 

The  level  remains  constant  although  the  bring  about  the  changes, 
water  is  continually  changing;  suggestive  The  addition  of  Various 
of  the  changes  in  the  blood.  materials  to  the  blood 

just  equals  the  withdrawal  of  the  same  materials  from  the 
blood.  Somewhat  as  a  vessel  of  water  (Fig.  12)  having 
an  inflow  and  an  outflow  which  are  equal  in  amount  may 
keep  always  at  the  same  level,  the  balancing  of  the  intake 
and  outgo  of  the  blood  keeps  its  composition  about  the 
same  from  time  to  time. 

Hygiene  of  the  Blood.  —  The  blood,  being  a  changeable 
liquid,  is  easily  affected  through  our  habits  of  living. 
Since  it  may  be  affected  for  ill  as  well  as  for  good,  one 

1  Certain  substances,  called  opsonins,  have  recently  been  shown  to  exist  in  the 
plasma,  that  aid  the  white  corpuscles   in  their  work  of  destroying  germs.    The 
opsonins  appear  to  act  in  such  a  manner  as  to  weaken  the  germs  and  make  them 
more  susceptible  to  the  attacks  of  the  white  corpuscles. 

2  Some  of  the  changes    in  the  blood  are  very  closely  related  to  our  everyday 
habits  and  inclinations'.     For  example,  a  lack  of  nourishment  in  the  blood  causes 
hunger  and  this  leads  to  the  taking  of  food.      If  the  fluids  of  the  body  become 
too  dense,  a  feeling  of  thirst  is  aroused  which  prompts  one  to  drink  water. 


THE   BLOOD  35 

should  cultivate  those  habits  that  are  beneficial  and  avoid 
those  that  are  harmful  in  their  effects.  Most  of  the 
hygiene  of  the  blood,  however,  is  properly  included  in 
the  hygiene  of  the  organs  that  act  upon  the  blood  —  a  fact 
which  makes  it  unnecessary  to  treat  this  subject  fully  at 
this  time. 

From  a  health  standpoint,  the  most. important  constitu- 
ents of  the  blood  are,  perhaps,  the  corpuscles.  These  are 
usually  sufficient  in  number  and  vigor  in  the  blood  of  those 
who  take  plenty  of  physical  exercise,  accustom  them- 
selves to  outdoor  air  and  sunlight,  sleep  sufficiently,  and 
avoid  the  use  of  injurious  drugs.  On  the  other  hand, 
they  are  deficient  in  quantity  and  inferior  in  quality  in 
the  bodies  of  those  who  pursue  an  opposite  course.  Im- 
purities not  infrequently  find  their  way  into  the  blood 
through  the  digestive  organs.'  One  should  eat  wholesome, 
well-cooked  food,  drink  freely  of  pure  water,  and  limit  the 
quantity  of  food  to  what  can  be  properly  digested.  The 
natural  purifiers  of  the  blood  are  the  organs  of  excretion. 
The  skin  is  one  of  these  and  its  power  to  throw  off  impu- 
rities depends  upon  its  being  clean  and  active. 

Effect  of  Drugs.  —  Certain  drugs  and  medicines,  includ- 
ing alcohol  and  quinine,1  have  recently  been  shown  to 
destroy  the  white  corpuscles.  The  effect  of  such  sub- 
stances, if  introduced  in  considerable  amount  in  the  body, 
is  to  render  one  less  able  to  withstand  attacks  of  disease. 
Many  patent  medicines  are  widely  advertised  for  purifying 
the  blood.  While  these  may  possibly  do  good  in  particu- 
lar cases,  the  habit  of  doctoring  one's  self  with  them  is 
open  to  serious  objection.  Instead  of  taking  drugs  and 
patent  medicines  for  purifying  the  blood,  one  should  study 
to  live  more  hygienically.  We  may  safely  rely  upon 

1  Metchnikoff,  The  New  Hygiene. 


36  THE   VITAL   PROCESSES 

wholesome  food,  pure  water,  outdoor  exercise  and  sunlight, 
plenty  of  sleep,  and  a  clean  skin  for  keeping  the  blood  in 
good  condition.  If  these  natural  remedies  fail,  a  physician 
should  be  consulted. 

Summary.  —  The  blood  is  the  carrying  or  transporting 
agent  of  the  body.  It  consists  in  part  of  constituents,  such 
as  the  red  corpuscles,  that  enable  it  to  carry  different  sub- 
stances ;  and  in  part  of  the  materials  that  are  being  carried. 
The  latter,  which  include  food  and  oxygen  for  the  cells  and 
wastes  from  the  cells,  may  be  classed  as  freight.  Certain 
constituents  in  the  blood  destroy  disease  germs,  and  other 
constituents,  by  coagulating,  close  small  leaks  in  the  blood 
vessels.  Although  subject  to  rapid  and  continuous  change, 
the  blood  is  able  — by  reason  of  the  balancing  of  materials 
added  to  'and  withdrawn  from  it  —  to  remain  about  the 
same  in  quantity  and  composition. 

Exercises.  —  i .  Compare  blood  and  water  with  reference  to  weight, 
density,  color,  odor,  and  complexity  of  composition. 

2.  Show  by  an  outline  the  different  constituents  of  the  blood. 

3.  Compare   the  red  and   white  corpuscles  with  reference  to  size, 
shape,  number,  origin,  and  function. 

4.  Name  some  use  or  purpose  for  each  constituent  of  the  blood. 

5.  What  constituents  of  the  blood  may  be  regarded  as  freight  and 
what  as  agents  for  carrying  this  freight  ? 

6.  After  coagulation,  what  portions  of  the  blood  are  found  in  the 
clot  ?     What  portions  are  found  in  the  serum  ? 

7.  What  purposes  are  served  by  water  in  the  blood  ? 

8.  Show  how  the  blood,  though  constantly  changing,  is  kept  about . 
the  same  in  quantity,  density,  and  composition. 

9.  In  the  lungs  the  blood  changes  from  a  dark  to  a  bright  red  color 
and  in  the  tissues  it  changes  back  to  dark  red.     What  is  the  cause  of 
these  changes  ? 

10.  If  the  oxygen  and   hemoglobin  formed  a  strong  instead  of  a 
weak  chemical  union,  could  the  hemoglobin  then  act  as  an  oxyaen  car- 
rier ?     Why  ? 


THE   BLOOD 


37 


1 1 .  What  habits  of  living  favor  the  development  of  corpuscles  in 
the  blood  ? 

12.  Why  will  keeping  the  skin  clean  and  active  improve  the  quality 
of  one's  blood  ?  ^x^ 

PRACTICAL  WORK 

monstrate   the   Physical   Properties   of   Blood    (Optional) 

Since  blood  is  needed  in  considerable  quantity  in  the  following  experi- 
ments, it  is  best  obtained  from  the  butcher.  To  be  sure  of  securing  the 
blood  in  the  manner  desired,  take  to  the  butcher  three  good-sized 
bottles  bearing  labels  as  follows  : 


Fill  two  thirds  full. 
While  the  blood  is 
cooling,  stir  rapidly 
with  the  hand  or  a 
bunch  of  switches  to 
remove  the  clot. 


Fill  two  thirds  full 
and  set  aside  without 
shaking  or  stirring. 


Fill  two  thirds  full 
and  thoroughly  mix 
with  the  liquid  in  the 
bottle. 


Label  3  must  be  pasted  on  a  bottle,  having  a  tight-fitting  stopper, 
which  is  filled  one  fifth  full  of  a  saturated  solution  of  Epsom  salts.  The 
purpose  of  the  salts  is  to  prevent  coagulation  until  the  blood  is  diluted 
with  water  as  in  the  experiments  which  follow. 

Experiments. —  i.  Let  some  of  the  defibrinated  blood  (bottle  i) 
flow  (not  fall)  on  the  surface  of  water  in  a  glass  vessel.  Does  it  remain 
on  the  surface  or  sink  to  the  bottom  ?  What  does  the  experiment 
show  with  reference  to  the  relative  weight  of  blood  and  water  ? 

2.  Fill  a  large  test  tube  or  a  small  bottle  one  fourth  full  of  the  defi- 
brinated blood  and  thin  it  by  adding  an  equal  amount  of  water.     Then 
place  the  hand  over  the  mouth  and  shake  until  the  blood  is  thoroughly 
mixed  with  the  air.     Compare  with  a  portion  of  the  blood  not  mixed 
with  the  air,  noting  any  difference  in  color.     What  substance  in  the  air 
has  acted  on  the  blood  to  change  its  color  ? 

3.  Fill  three  tumblers  each  two  thirds  full  of  water  and  set  them  in 
a  \srarm  place.     Pour  into  one  of  the  tumblers,  and  thoroughly  mix  with 
the  water,  two  tablespoonfuls  of  the  blood  containing  the  Epsom  salts. 
After  an  interval  of  half  an  hour  add  blood  to  the  second  tumbler  in  the. 


38  THE   VITAL   PROCESSES 

same  manner,  and  after  another  half  hour  add  blood  to  the  third.  The 
water  dilutes  the  salts  so  that  coagulation  is  no  longer  prevented.  Jar 
the  vessel  occasionally  as  coagulation  proceeds  ;  and  if  the  clot  is  slow 
in  forming,  add  a  trace  of  some  salt  of  calcium  (calcium  chloride).  After 
the  blood  has  been  added  to  the  last  tumbler  make  a  comparative  study 
of  all.  Note  that  coagulation  begins  in  all  parts  of  the  liquid  at  the 
same  time  and  that,  as  the  process  goes  on,  the  clot  shrinks  and  is 
drawn  toward  the  center. 

4.  Place  a  clot  from  one  of  the  tumblers  in  experiment  3  in  a  large 
vessel  of  water.     Thoroughly  wash,  adding  fresh  water,  until  a  white, 
stringy  solid  remains.     This  substance  is  fibrin. 

5.  Examine  the  coagulated  blood  obtained  from  the  butcher  (bottle 
2).     Observe  the  dark  central  mass  (the  clot)  surrounded  by  a  clear 
liquid  (the  serum).     Sketch  the  vessel  and  its  contents,  showing  and 
naming  the  parts  into  which  the  blood  separates  by  coagulation. 

To  examine  the  Red  Corpuscles.  —  Blood  for  this  purpose  is  easily 
obtained  from  the  finger.  With  a  handkerchief,  wrap  one  of  the  fingers 
of  the  left  hand  from  the  knuckle  down  to  the  first  joint.  Bend  this 
joint  and  give  it  a  sharp  prick  with  the  point  of  a  sterilized  needle  just 
above  the  root  of  the  nail.  Pressure  applied  to  the  under  side  of  the 
finger  will  force  plenty  of  blood  through  a  very  small  opening.  (To 
prevent  any  possibility  of  blood  poisoning  the  needle  should  be  steril- 
ized. This  may  be  done  by  dipping  it  in  alcohol  or  by  holding  it  for  an 
instant  in  a  hot  flame.  It  is  well  also  to  wash  the  finger  with  soap  and 
water,  or  with  alcohol,  before  the  operation.)  Place  a  small  drop  of  the 
blood  in  the  middle  of  a  glass  slide,  protect  the  same  with  a  cover  glass, 
and  examine  with  a  compound  microscope.  At  least  two  specimens 
should  be  examined,  one  of  which  should  be  diluted  with  a  little  saliva 
or  a  physiological  salt  solution.1  In  the  diluted  specimen  the  red  cor- 
puscles appear  as  amber-colored,  circular,  disk-shaped  bodies.  In  the 
undiluted  specimen  they  show  a  decided  tendency  to  arrange  them- 
selves in  rows,  resembling  rows  of  coins.  (Singly,  the  corpuscles  do 
not  appear  red  when  highly  magnified.) 

A  few  white  corpuscles  may  generally  be  found  among  the  red  ones 
in  the  undiluted  specimen.  These  become  separated  by  the  formation 

1  A  physiological  salt  solution  is  prepared  by  dissolving  .6  of  a  gram  of  common 
salt  in  too  cc.  of  distilled  water  or  pure  cistern  water.  This  solution,  having  the 
same  density  as  the  plasma  of  the  blood,  does  not  act  injuriously  upon  the 
corpuscles. 


THE    BLOOD  39 

of  the  red  corpuscles  into  rows.  They  are  easily  recognized  by  their 
larger  size  and  by  their  silvery  appearance,  due  to  the  light  shining 
through  them. 

To  examine  White  Corpuscles.  —  Obtain  from  the  butcher  a  small 
piece  of  the  neck  sweetbread  of  a  calf.  Press  it  between  the  fingers 
to  squeeze  out  a  whitish,  semi-liquid  substance.  Dilute  with  physiolog- 
ical salt  solution  on  a  glass  slide  and  examine  with  a  compound  micro- 
scope. Numerous  white  corpuscles  of  different  kinds  and  sizes  will  be 
found.  Make  sketches. 

To  prepare  Models  of  Red  Corpuscles.  —  Several  models  of  red 
corpuscles  should  be  prepared  for  the  use  of  the  class.  Clay  and  putty 
may  be  pressed  into  the  form  of  red  corpuscles  and  allowed  to  harden, 
and  small  models  may  be  cut  out  of  blackboard  crayon.  Excellent 
models  can  be  molded  from  plaster  of  Paris  as  follows :  Coat  the 
inside  of  the  lid  of  a  baking  powder  can  with  oil  or  vaseline  and  fill  it 
even  full  of  a  thick  mixture  of  plaster  of  Paris  and  water.  After  the 
plaster  has  set,  remove  it  from  the  lid  and  with  a  pocket-knife  round  off 
the  edges  and  hollow  out  the  sides  until  the  general  form  of  the  cor- 
puscle is  obtained.  The  models  may  be  colored  red  if  it  is  desired  to 
match  the  color  as  well  as  the  form  of  the  corpuscle. 


CHAPTER  V 
THE  CIRCULATION 

A  CARRIER  must  move.  To  enable  the  blood  to  carry  food 
and  oxygen  to  the  cells  and  waste  materials  from  the  cells, 
and  also  to  distribute  heat,  it  is  necessary  to  keep  it  mov- 
ing, or  circulating,  in  all  parts  of  the  body.  So  closely 
related  to  the  welfare  of  the  body  is  the  circulation 1  of  the 
blood,  that  its  stoppage  for  only  a  brief  interval  of  time 
results  in  death. 

Discovery  of  the  Circulation.  —  The  discovery  of  the  circulation  of 
the  blood  was  made  about  1616  by  an  English  physician  named  Harvey. 
In  1619  he  announced  it  in  his  public  lectures  and  in  1628  he  published 
a  treatise  in  Latin  on  the  circulation.  The  chief  arguments  advanced 
in  support  of  his  views  were  the  presence  of  valves  in  the  heart  and 
veins,  the  continuous  movement  of  the  blood  in  the  same  direction 
through  the  blood  vessels,  and  the  fact  that  the  blood  comes  from  a  cut 
artery  in  jets,  or  spurts,  that  correspond  to  the  contractions  of  the  heart. 

No  other  single  discovery  with  reference  to  the  human  body  has 
proved  of  such  great  importance.  A  knowledge  of  the  nature  and  pur- 
pose of  the  circulation  was  the  necessary  first  step  in  understand- 
ing the  plan  of  the  body  and  the  method  of  maintaining  life,  and 
physiology  as  a  science  dates  from  the  time  of  Harvey's  discovery. 

Organs  of  Circulation. — The  organs  of  circulation,  or 
blood  vessels,  are  of  four  -kinds,  named  the  heart,  the 
arteries,  the  capillaries,  and  the  veins.  They  serve  as  con- 

1  The  term  "  circulation  "  literally  means  moving  in  a  circle.  While  the  blood 
does  not  move  through  the  body  in  a  circle,  the  term  is  justified  by  the  fact  that 
the  blood  flows  out  continually  from  a  single 'point,  the  heart,  and  to  this  point  is 
continually  returning. 

40 


THE   CIRCULATION 


trivances  both  for  holding  the  blood  and  for  keeping  it  in 
motion  through  the  body.  The  heart,  which  is  the  chief 
organ  for  propelling  the  blood,  acts  as  a  force  pump, 
while  the  arteries  and  veins  serve  as  tubes  for  conveying 
the  blood  from  place  to  place.  Moreover,  the  blood  vessels 
are  so  connected  that  the  blood  moves  through  them  in  a 
regular  order,  performing  two  well-defined  circuits. 

The  Heart.  —  The  human  heart,  roughly  speaking,  is 
about  the  size  of  the  clenched  fist  of  the  individual  owner. 
It  is  situated  very  near 
the  center  of  the  tho- 
racic cavity  and  is  almost 
completely  surrounded 
by  the  lungs.  It  is  cone- 
shaped  and  is  so  sus- 
pended that  the  small 
end  hangs  downward, 
forward,  and  a  little  to 
the  left.  When  from  ex- 
citement, or  other  cause, 
one  becomes  conscious 
of  the  movements  of  the 
heart,  these  appear  to 
be  in  the  left  portion  of 
the  chest,  a  fact  which  FIG.  13.— Heart  in  position  in  thoracic 

cavity.     Dotted  lines  show  position  of  dia- 
accounts    for  the   errone-     phragm  and  of  margins  of  lungs. 

ous  impression  that  the 

heart  is  on   the  left  side.     The  position  of  the  heart  in 

the  cavity  of  the  chest  is  shown  in  Fig.   13. 

The  Pericardium.  —  Surrounding  the  heart  is  a  protec- 
tive covering,  called  the  pericardium.  This  consists  of  a 
closed  membranous  sac  so  arranged  as  to  form  a  double 
covering  around  the  heart.  The  heart  does  not  lie  inside 


42 


THE   VITAL   PROCESSES 


of  the  pericardial  sac,  as  seems  at  first  glance  to  be  the 
case,  but  its  relation  to  this  space  is  like  that  of  the  hand 
to  the  inside  of  an  empty  sack  which  is  laid  around  it 
(Fig.  14).  The  inner  layer  of  the  pericardium  is  closely 
attached  to  the  heart  muscle,  forming  for  it  an  outside  cov- 
ering. The  outer  layer  hangs  loosely 
around  the  heart  and  is  continuous 
with  the  inner  layer  at  the  top.  The 
outer  layer  also  connects  at  certain 
places  with  the  membranes  surround- 
ing the  lungs  and  is  attached  below 
to  the  diaphragm.  Between  the  two 
layers  of  the  pericardium  is  secreted 
a  liquid  which  prevents  friction  from 
the  movements  of  the  heart. 

Cavities   of  the  Heart.  —  The  heart 
is  a  hollow,  muscular  organ  which  has 
moved.    A.  Place  occu-   jts  interior  divided  by  partitions  into 

pied  by   the   heart.     B.     .  «•-.«  •„•  --^i 

Space  inside  of  perkar-   four  distinct  cavities.     The  mam  par- 
dial  sac.    a.  inner  layer   tition  extends  from  top  to  bottom  and 

of  pericardium  and  outer     diyides  the  heart  into   two   similar   por- 
lining  of  heart,    b.  Outer 

tions,  named  from  their  positions  the 
right  side  and  the  left  side.  On  each 
side  are  two  cavities,  the  one  being  di- 
rectly above  the  other.  The  upper  cavities  are  called  auri- 
cles and  the  lower  ones  ventricles.  To  distinguish  these 
cavities  further,  they  are  named  from  their  positions  the 
right  auricle  and  the  left  auricle,  and  the  right  ventricle 
and  the  left  ventricle  (Fig.  15).  The  auricles  on  each  side 
communicate  with  the  ventricles  below ;  but  after  birth  there 
is  no  communication  between  the  cavities  on  the  opposite 
sides  of  the  heart.  All  the  cavities  of  the  heart  are  lined 
with  a  smooth,  delicate  membrane,  called  the  endocardium. 


D 

FIG.  14.  —  Diagram 
of  section  of  the  peri- 
cardial sac,  heart  re- 


layer  of  pericardium. 
Covering  of  lung. 
Diaphragm. 


THE   CIRCULATION 


43 


Valves  of  the  Heart.  —  Located  at  suitable  places  in  the 
heart  are  four  gate-like  contrivances,  called  valves.  The 
purpose  of  these  is  to  give  the 
blood  a  definite  direction  in  its 
movements.  They  consist  of 
tough,  inelastic  sheets  of  con- 
nective tissue,  and  are  so  placed 
that  pressure  on  one  side  causes 
them  to  come  together  and  shut 
up  the  passageway,  while  pres- 
sure on  the  opposite  side  causes 
them  to  open.  A  valve  is  found 
at  the  opening  of  each  auricle 

into    the   ventricle,    and    at  the      .  Fir,  15. -Diagram  showing 

plan   of  the   heart,     i.  Semi- 
opening    of    each    ventricle    into     lunar  valves.    2.  Tricuspid  valve. 

the    artery    with    which    it 
connected. 


is 


rior  vena  cava.  10.  Superior 
venacava.  II.  Pulmonary  artery. 
12.  Aorta.  13.  Pulmonary  veins. 


3.  Mitral  valve.     4.  Right  auri- 
cle.    5.  Left    auricle.     6.  Right 
ventricle.        7.    Left     ventricle. 
The   Valve   between    the   right     8.  Chordae    tendinese.      9.  Infe- 

auricle  and  the  right  ventricle 
is  called  the  tricuspid  valve.  It 
is  suspended  from  a  thin  ring 
of  connective  tissue  which  surrounds  the  opening,  and 
its  free  margins  extend  into  the  ventricle  (Fig.  16).  It 
consists  of  three  parts,  as  its  name  implies,  which  are 
thrown  together  in  closing  the  opening.  Joined  to  the 
free  edges  of  this  valve  are  many  small,  tendinous  cords 
which  connect  at  their  lower  ends  with  muscular  pillars  in 
the  walls  of  the  ventricle.  These  are  known  as  the  chorda 
tendinea,  or  heart  tendons.  Their  purpose  is  to  serve  as 
valve  stops,  to  prevent  the  valve  from  being  thrown,  by  the 
force  of  the  blood  stream,  back  into  the  auricle. 

The  mitral,  or  bicuspid,  valve  is  suspended  around  the 
opening  between  the  left   auricle  and   the  left  ventricle, 


44 


THE   VITAL   PROCESSES 


-B 


with  the  free  margins  extending  into  the  ventricle.     It  is 
exactly  similar  in  structure  and  arrangement  to  the  tricus- 

pid  valve,  except  that  it  is 
stronger  and  is  composed  of 
two  parts  instead  of  three. 

The  right  semilunar  valve 
is  situated  around  the  open- 
ing of  the  right  ventricle 
into  the  pulmonary  artery. 
It  consists  of  three  pocket- 
shaped  strips  of  connective 
tissue  which  hang  loosely 
from  the  walls  when  there 
is  no  pressure  from  above ; 
but  upon  receiving  pressure, 
the  pockets  fill  and  project 
into  the  opening,  closing  it 
completely  (Fig.  16).  The 
left  semilunar  valve  is 
around  the  opening  of  the 
left  ventricle  into  the  aorta, 
and  is  similar  in  all  respects  to  the  right  semilunar  valve. 

Differences  in  the  Parts  of  the  Heart.  —  Marked  differ- 
ences are  found  in  the  walls  surrounding  the  different 
cavities  of  the  heart.  The  walls  of  the  ventricles  are  much 
thicker  and  stronger  than  those  of  the  auricles,  while  the 
walls  of  the  left  ventricle  are  two  or  three  times  thicker 
than  those  of  the  right.  A  less  marked  but  similar  differ- 
ence exists  between  the  auricles  and  also  between  the 
valves  on  the  two  sides  of  the  heart.  These  differences 
in  structure  are  all  accounted  for  by  the  work  done  by  the 
different  portions  of  the  heart.  The  greater  the  work,  the 
heavier  the  structures  that  perform  the  work. 


FIG.  1 6.  — Right  side  of  heart 
dissected  to  show  cavities  and  valves. 
B.  Right  semilunar  valve.  The  tri- 
cuspid  valve  and  the  chordse  tendineae 
shown  in  the  ventricle. 


THE   CIRCULATION 


45 


Connection  with  Arteries  and  Veins.  — Though  the  heart 
is  in  communication  with  all  parts  of  the  circulatory  system, 
it  makes  actual  connection  with  only 
a  few  of  the  blood  tubes.  These 
enter  the  heart  at  its  upper  portion 
(Fig.  15),  but  connect  with  its  differ- 
ent cavities  as  follows : 

1.  With    the     right    auricle,    the 
superior  and  the  inferior  venae  cavae 
and  the  coronary  veins.     The  supe- 
rior vena  cava  receives  blood  from 
the  head  and  the  upper  extremities ; 
the   inferior    vena    cava,    from    the 
trunk    and    the    lower    extremities ; 
and   the   coronary   veins,   from    the 
heart  itself. 

2.  With  the  left  auricle,  the  four 
pulmonary    veins.       These    receive 
blood  from  the  lungs  and  empty  it 
into  the  left  auricle. 

3.  With   the   right   ventricle,   the    the  circ«lation'    . 

in  general  the  work  done 

pulmonary  artery.  This  receives  by  each  part  of  the  heart, 
blood  from  the  heart  and  by  its  The  r'gbt  ventricle  forces 

i  ,  ,.   .    M  ..  ,,  the     blood     through    the 

branches  distributes  it  to  all  parts    lungs  and   into  g   kft 

Of  the  lungs.  auricle.     The  left  ventricle 

4.  With  the  left  ventricle,  the  aorta.    forces  blood   *hrough  all 

„,  .  parts  of  the  body  and  back 

The  aorta  receives  blood  from  the  to  the  right  auricle>  The 
heart  and  through  its  branches  de-  auricles  force  blood  into 
livers  it  to  all  parts  of  the  body.  the  ventricles- 

How  the  Heart  does  its  Work.  —  The  heart  is  a  muscular 
pump1  and  does  its  work  through  the   contracting  and 


FIG.  17.  —  Diagram  of 


1  The  heart  at  first  glance  seems  to  bear  little  resemblance  to  the  pumps  in 
common   use.     When   it   is   remembered,  however,  that  any  contrivance  which 


THE   VITAL   PROCESSES 


relaxing  of  its  walls.  During  contraction  the  cavities  are 
closed  and  the  blood  is  forced  out  of  them.  During  relax- 
ation  the  cavities  open  and  are  refilled.  The  valves  direct 
the  flow  of  the  blood,  being  so  arranged  as  to  keep  it 
moving  always  in  the  same  direction  (Fig.  17). 

The  heart,  however,  is  not  a  single  or  a  simple  pump, 
but  consists  in  reality  of  four  pumps  which  correspond  to 
its  different  cavities.  These  connect  with  each  other  and 
with  the  blood  vessels  over  the  body  in  such  a  manner 
that  each  aids  in  the  general  movement  of  the  blood. 

Work  of  Auricles  and  Ventricles  Compared.  —  In  the  work 
of  the  heart  the  two  auricles  contract  at  the  same  time  — 
their  contraction  being  followed  imme- 
diately by  the  contraction  of  both  ven- 
tricles. After  the  contraction  of  the 
ventricles  comes  a  period  of  rest,  or 
relaxation,  about  equal  in  time  to  the 
period  of  contraction  of  both  the  auri- 
cles and  the  ventricles.1  On  account 
of  the  work  which  they  perform,  the 
auricles  have  been  called  the  "  feed 
pumps  "  of  the  heart ;  and  the  ventri- 
cles, the  "  force  pumps."  2  It  is  the 
function  of  the  auricles  to  collect  the  blood  from  the  veins, 
to  let  this  run  slowly  into  the  ventricles  when  both  the 

moves  a  fluid  by  varying  the  size  of  a  cavity  is  a  pump,  it  is  seen  that  not  only 
the  heart,  but  the  chest  in  breathing  and  also  the  mouth  in  sucking  a  liquid  through 
a  tube,  are  pumps  in  principle.  The  ordinary  syringe  bulb  illustrates  the  class  of 
pumps  to  which  the  heart  belongs.  (See  Practical  Work.) 

1  The  contraction  of  the  heart  is  known  as  the  systole  and  its  relaxation  as  the 
diastole.    The  systole  plus  the  diastole  forms  the  so-called  "cardiac  cycle''   (Fig. 
18).    This  consists  of  (i)  the  contraction  of  the  auricles,  (2)  the  contraction  of  the 
ventricles,  and  (3)  the  period  of  rest.     The  heart  systole  includes  the  contraction 
of  both  the  auricles  and  the  ventricles. 

2  Martin,  The  Human  Body. 


FIG.  1 8.  —  Diagram 
illustrating  the  "  cardiac 
cycle." 


THE   CIRCULATION  47 

auricles  and  ventricles  are  relaxed,  and  finally,  by  contract- 
ing, to  force  an  excess  of  blood  into  the  ventricles,  thereby 
distending  their  walls.  The  ventricles,  having  in  this  way 
been  fully  charged  by  the  auricles,  now  contract  and  force 
their  contents  into  the  large  arteries. 

Sounds  of  the  Heart.  —  Two  distinct  sounds  are  given  out  by  the  heart 
as  it  pumps  the  blood.  One  of  them  is  a  dull  and  rather  heavy  sound, 
while  the  other  is  a  short,  sharp  sound.  The  short  sound  follows 
quickly  after  the  dull  sound  and  the  two  are  fairly  imitated  by  the 
words  "'lubb,  diip."  While  the  cause  of  the  first  sound  is  not  fully 
understood,  most  authorities  believe  it  to  be  due  to  the  contraction  of 
the  heart  muscie  and  the  sudden  tension  on  the  valve  flaps.  The  second 
sound  is  due  to  the  closing  of  the  semilunar  valves.  These  sounds  are 
easily  heard  by  placing  an  ear  against  the  chest  wall.  They  are  of  great 
value  to  the  physician  in  determining  the  condition  of  the  heart. 

Arteries  and  Veins.  —  These  form  two  systems  of  tubes 
which  reach  from  the  heart  to  all  parts  of  the  body.  The 
arteries  receive  blood  from  the  heart  and  distribute  it  to 
the  capillaries.  The  veins  receive  the  blood  from  the 
capillaries  and  return  it  to  the  heart.  The  arteries  and 
veins  are  similar  in  structure,  both  having  the  form  of 
tubes  and  both  having  three  distinct  layers,  or  coats,  in 
their  walls.  The  corresponding  coats  in  the  arteries  and 
veins  are  made  up  of  similar  materials,  as  follows : 

1.  The  inner  coat  consists  of  a  delicate  lining  of  flat 
cells  resting  upon  a  thin  layer  of  connective  tissue.     The 
inner  coat  is  continuous  with  the  lining  of  the  heart  and 
provides  a  smooth   surface  over  which  the  blood  glides 
with  little  friction. 

2.  The  middle  coat  consists  mainly  of  non-striated,  or 
involuntary,  muscular  fibers.     This  coat  is  quite  thin  in 
the  veins,  but  in  the  arteries  it  is  rather  thick  and  strong. 

3.  The  outer  coat  is  made  up  of  a  variety  of  connective 


48 


THE  VITAL  PROCESSES 


FIG.  19.— Ar- 
tery dissected  to 
show  the  coats. 


tissue  and  is  also  much  thicker  and  stronger 
in  the  arteries  than  in  the  veins. 

Marked  differences  exist  between  the 
arteries  and  the  veins,  and  these  vessels 
are  readily  distinguished  from  each  other. 
The  walls  of  the  arteries  are  much  thicker 
and  heavier  than  those  of  the  veins  (Fig. 
19).  As  a  result  these  tubes  stand  open 
when  empty,  whereas  the  veins  collapse. 
The  arteries  also  are  highly  elastic,  while 
the  veins  are  but  slightly  elastic.  On  the 
other  hand,  many  of  the  veins  contain 
valves,  formed  by  folds  in  the  inner  coat 
(Fig.  20),  while  the  arteries  have  no 
valves.  The  blood  flows  more  rapidly  through  the  arte- 
ries than  through  the  veins,  the  difference  being  due  to 
the  fact  that  the  system  of  veins  has 
a  greater  capacity  than  the  system  of 
arteries. 

Why  the  Arteries  are  Elastic.  —  The 
elasticity  of  the  arteries  serves  a  twofold 
purpose.  It  keeps  the  arteries  from 
bursting  when  the  blood  is  forced  into 
them  from  the  ventricles,  and  it  is  a 
means  of  supplying  pressure  to  the  blood 
while  the  ventricles  are  in  a  condition  of 
relaxation.  The  latter  purpose  is  accom- 
plished as  follows : 

Contraction  of  the  ventricles  fills  the        FIG.    20.  —  Vein 
arteries  overfull,  causing  them  to  swell    *P1!t   open  to  show 

,  ,  the  valves. 

out  and    make   room  for  the  excess  of 

blood.     Then  while  the  ventricles  are  resting  and  filling, 

the  stretched  arteries  press  upon  the  blood    to  keep  it 


THE   CIRCULATION  49 

flowing  into  the  capillaries.  In  this  way  they  cause  the 
intermittent  flow  from  the  heart  to  become  a  steady  stream 
in  the  capillaries. 

The  swelling  of  the  arteries  at  each  contraction  of  the 
ventricle  is  easily  felt  at  certain  places  in  the  body,  such 
as  the  wrist.  This  expansion,  known  as  the  "pulse,"  is 
the  chief  means  employed  by  the  physician  in  determining 
the  force  and  rapidity  of  the  heart's  action. 

Purpose  of  the  Valves  in  the  Veins.  —  The  valves  in  the 
veins  are  not  used  for  directing  the  general  flow  of  the 
blood,  the  valves  of  the  heart  being  sufficient  for  this  pur- 
pose. Their  presence  is  necessary  because  of  the  pressure 
to  which  the  veins  are  subjected  in  different  parts  of  the 
body.  The  contraction  of  a  muscle  will,  for  example,  close 
the  small  veins  in  its  vicinity  and  diminish  the  capacity 
of  the  larger  ones.  The  natural  tendency  of  such  pressure 
is  to  empty  the  veins  in  two  directions  —  one  in  the  same 
direction  as  the  regular  movement  of  the  blood,  but  the 
other  in  the  opposite  direction.  The  valves  by  closing 
cause  the  contracting  muscle  to  push  the  blood  in  one 
direction  only  —  toward  the  heart.  The  valves  in  the  veins 
are,  therefore,  an  economical  device  for  enabling  variable 
pressure  in  different  parts  of  the  body  to  assist  in  the  cir- 
culation. Veins  like  the  inferior  vena  cava  and  the  veins  of 
the  brain,  which  are  not  compressed  by  movements  of  the 
body,  do  not  have  valves. 

Purposes  of  the  Muscular  Coat.  —  The  muscular  coat, 
which  is  thicker  in  the  arteries  than  in  the  veins  and  is 
more  marked  in  small  arteries  than  in  large  ones,  serves 
two  important  purposes.  In  the  first  place  it,  together 
with  the  elastic  tissue,  keeps  the  capacity  of  the  blood 
vessels  equal  to  the  volume  of  the  blood.  Since  the  blood 
vessels  are  capable  of  holding  more  blood  than  may  be 


THE   VITAL   PROCESSES 


present  at  a  given  time  in  the  body,  there  is  a  liability  of 
empty  spaces  occurring  in  these  tubes.  Such  spaces  would 
seriously  interfere  with  the  circulation,  since  the  heart  pres- 
sure could  not  then  reach  all  parts  of  the  blood  stream. 
This  is  prevented  by  the  contracted  state,  or  "tone,"  of 
the  blood  vessels,  due  to  the  muscular  coat. 

In  the  second  place,  the  muscular  coat  serves  the  pur- 
pose of  regulating  the  amount  of  blood  which  any  given 
organ  or  part  of  the  body  receives.  This  it  does  by  vary- 
ing the  caliber  of  the  arteries  going  to  the  organ  in  ques- 
tion. To  increase  the  blood  supply,  the  muscular  coat 
relaxes.  The  arteries  are  then  dilated  by  the  blood  pres- 
sure from  within  so  as  to  let  through  a  larger  quantity  of 
blood.  To  diminish  the  supply,  the  muscle  contracts, 
making  the  caliber  of  the  arteries  less,  so  that  less  blood 
can  flow  to  this  part  of  the  body.  Since  the  need  of 
organs  for  blood  varies  with  their  activity,  the  muscular 
coat  serves  in  this  way  a  very  necessary  purpose. 

Capillaries.  —  The  capillaries  consist  of   a  network  of 

minute  blood  ves- 
sels which  connect 
the  terminations 
of  the  smallest 
arteries  with  the 
beginnings  of  the 
smallest  veins 
(Fig.  21).  They 
FIG.  21.— Diagram  of  net  work  of  capillaries  have  an  average 

between  a  very  small  artery  and  a  very  small  vein.  A-  f     , 

Shading  indicates  the  change  of  color  of  the  blood  diameter     of     ^88 

as  it  passes  through  the  capillaries.     S.    Places  be-  than  One  tWO-thoU- 

tween  capillaries  occupied  by  the  cells.  sandth   of  an  jnch 

(12  p)  and  an  average  length  of  less  than  one  twenty-fifth 
of  an  inch  (i  millimeter).     Their  walls  consist  of  a  single 


bet 


THE   CIRCULATION  51 

coat  which  is  continuous  with  the   lining  of  the  arteries 
and   veins.       This   coat   is    formed  of  a   single  layer   of 

thin,    fiat    cells    placed    edge    to    edge     ____^__ 

(Fig.  22).     With  a  few  exceptions,  the 
capillaries  are  found  in  great  abundance 

in  all  parts  of  the  body. 

_,       „ .  ,     ,.        f.     .„     .  ~  FIG.  22.  —  Surface 

Functions    of    the    Capillaries.  —  On    of    capiuary  highly 

account  of  the  thinness  of  their  walls,    magnified,  showing  its 
the  capillaries  are  able  to  serve  a  two-    c°at    **    thin    flls 

placed  edge  to  edge. 

told  purpose  in  the  body  : 

1.  They  admit  materials  into  the  blood  vessels. 

2.  They  allow  materials  to  pass  from  the  blood  vessels 
to  the  surrounding  tissues. 

When  it  is  remembered  that  the  blood,  as  blood,  does 
not  escape  from  the  blood  vessels  under  normal  conditions, 
the  importance  of  the  work  of  the  capillaries  is  apparent. 
To  serve  its  purpose  as  a  carrier,  there  must  be  places 
where  the  blood  can  load  up  with  the  materials  which  it  is 
to  carry,  and  places  also  where  these  can  be  unloaded. 
Such  places  are  supplied  by  the  capillaries. 

The  capillaries  also  serve  the  purpose  of  spreading  the 
blood  out  and  of  bringing  it  very  near  the  individual  cells 
in  all  parts  of  the  body  (Fig.  21). 

Functions  of  Arteries  and  Veins.  — While  the  capillaries  provide  the 
means  whereby  materials  may  both  enter  and  leave  the  blood,  the 
arteries  and  veins  serve  the  general  purpose  of  passing  the  blood  from 
one  set  of  capillaries  to  another.  Since  pressure  is  necessary  for  moving 
the  blood,  these  tubes  must  connect  with  the  source  of  the  pressure, 
which  is  the  heart.  In  the  arteries  and  veins  the  blood  neither  receives 
nor  gives  up  material,  but  having  received  or  given  up  material  at  one 
set  of  capillaries,  it  is  then  pushed  through  these  tubes  to  where  it  can 
serve  a  similar  purpose  in  another  set  of  capillaries  (Fig.  23). 

Divisions  of  the  Circulation.  —  Man,  in  common  with  all 
warm-blooded  animals,  has  a  double  circulation,  a  fact 


52  THE   VITAL  PROCESSES 

which  explains  the  double  structure  of  his  heart.  The 
two  divisions  are  known  as  the  pulmonary  and  the  systemic 
circulations.  By  the  former  the  blood  passes  from  the  right 
ventricle  through  the  lungs,  and  is  then  returned  to  the 
left  auricle ;  by  the  latter  it  passes  from  the  left  ventricle 
through  all  parts  of  the  body,  returning  to  the  right  auricle. 

The  general  plan  of  the  circulation  is  indicated  in  Fig. 
23.  All  the  blood  flows  continuously  through  both  circu- 
lations and  passes  the  various  parts  in  the  following  order  : 
right  auricle,  tricuspid  valve,  right  ventricle,  right  semi- 
lunar  valve,  pulmonary  artery  and  its  branches,  capillaries 
of  the  lungs,  pulmonary  veins,  left  auricle,  mitral  valve, 
left  ventricle,  left  semilunar  valve,  aorta  and  its  branches, 
systemic  capillaries,  the  smaller  veins,  superior  and  inferior 
venae  cavas,  and  then  again  into  the  right  auricle. 

In  the  pulmonary  capillaries  the  blood  gives  up  carbon 

•  dioxide  and  receives  oxygen,  changing  from  a  dark  red 

to  a  bright  red  color.     In  the  systemic  capillaries  it  gives 

up  oxygen,  receives  carbon  dioxide  and  other  impurities, 

and  changes  back  to  a  dark  red  color. 

In  addition  to  the  two  main  divisions  of  the  circulation, 
special  circuits  are  found  in  various  places.  Such  a  circuit 
in  the  liver  is  called  the  portal  circulation,  and  another  in 
the  kidneys  is  termed  the  renal  circulation.  To  some  extent 
the  blood  supply  to  the  walls  of  the  heart  is  also  outside  of 
the  general  movement ;  it  is  called  the  coronary  circulation. 

Blood  Pressure  and  Velocity.  —  The  blood,  in  obedience  to  physical 
laws,  passes  continuously  through  the  blood  vessels,  moving  always 
from  a  place  of  greater  to  one  of  less  pressure.  Through  the  contrac- 
tion of  the  ventricles,  a  relatively  high  pressure  is  maintained  in  the 
arteries  nearest  the  heart.1  This  pressure  diminishes  rapidly  in  the 

iThe  pressure  maintained  by  the  left  ventricle  has  been  estimated  to  be  nearly 
three  and  one  half  pounds  to  the  square  inch  — a  pressure  sufficient  to  sustain  a 
column  of  water  eight  feet  high.  The  pressure  maintained  by  the  right  ventricle  is 


THE  CIRCULATION 


53 


FIG.  23.  —  General  scheme  of  the  circulation,  showing 
places  where  the  blood  takes  on  and  gives  off  materials. 
I.  Body  in  general.  2.  Lungs.  3.  Kidneys.  4.  Liver. 
5.  Organs  of  digestion.  6.  Lymph  ducts.  7.  Pulmonary 
artery.  8.  Aorta. 


54 


THE   VITAL   PROCESSES 


small  arteries,  becomes  comparatively  slight  in  the  capillaries,  and  falls 
practically  to  nothing  in  the  veins.  Near  the  heart  in  the  superior  and 
inferior  vena  cavae,  the  pressure  at  intervals  is  said  to  be  negative. 
This  means  that  the  blood  from  these  veins  is  actually  drawn  into  the 
right  auricle  by  the  expansion  of  the  chest  walls  in  breathing.1 

The  velocity  of  the  blood  is  greatest  in  the  arteries,  less  in  the  veins, 
and  much  less  in  the  capillaries  than  in  either  the  arteries  or  the  veins. 
The  slower  flow  of  the  blood  through  the  capillaries  is  accounted  for  by 
the  fact  that  their  united  area  is  many  times  greater  than  that  of  the 
arteries  which  supply,  or  the  veins  which  relieve,  them.  This  allows 
the  same  quantity  of  blood,  flowing  through  them  in  a  given  time,  a 
wider  channel  and  causes  it  to  move  more  slowly.  The  time  required 
lor  a  complete  circulation  is  less  than  one  minute. 

Summary  of  Causes  of  Circulation.  —  The  chief  factor 
in  the  circulation  of  the  blood  is,  of  course,  the  heart.  The 
ventricles  keep  a  pressure  on  the  blood  which  is  sufficient 
to  force  it  through  all  the  blood  tubes  and  back  to  the 
auricles.  The  heart  is  aided  in  its  work  by  the  elasticity 
of  the  arteries,  which  keeps  the  blood  under  pressure  while 
the  ventricles  are  in  a  state  of  relaxation.  It  is  also  aided 
by  the  muscles  and  elastic  tissue  in  all  of  the  blood  vessels. 
These,  by  keeping  the  blood  vessels  in  a  state  of  "  tone,"  or 
so  contracted  that  their  capacity  just  equals  the  volume  of 
the  blood,  enable  pressure  from  the  heart  to  be  transmitted 
to  all  parts  of  the  blood  stream.  A  further  aid  to  the  circu- 
lation is  found  in  the  valves  in  the  veins,  which  enable  mus- 
cular contraction  within  the  body,  and  variable  pressure 
upon  its  surface,  to  drive  the  blood  toward  the  heart.  The 
heart  is  also  aided  to  some  extent  by  the  movements  of  the 
chest  walls  in  breathing.  The  organs  of  circulation  are 
under  the  control  of  the  nervous  system  (Chapter  XVIII). 

about  one  third  as  great.  In  maintaining  this  pressure  the  heart  does  a  work  equal 
to  about  one  two-hundredth  of  a  horse  power. 

1  The  location  of  the  heart  in  the  thoracic  cavity  causes  movements  of  the  chest 
walls  to  draw  blood  into  the  right  auricle  for  the  same  reason  that  they  "  draw  "  air 
into  the  lungs. 


THE   CIRCULATION  55 

HYGIENE  OF  THE   CIRCULATION 

Care  of  the  Heart.  —  The  heart,  consisting  largely  of 
muscle,  is  subject  to  the  laws  of  muscular  exercise.  It 
may  be  injured  by  over-exertion,  but  is  strengthened  by  a 
moderate  increase  in  its  usual  work.1  It  may  even  be  sub- 
jected to  great  exertion  without  danger,  if  it  be  trained  by 
gradually  increasing  its  work.  Such  training,  by  giving 
{he  heart  time  to  gain  in  size  and  strength,  prepares  it  for 
tasks  that  could  not  at  first  be  accomplished. 

In  taking  up  a  new  exercise  requiring  considerable  exer- 
tion, precautions  should  be  observed  to  prevent  an  over- 
strain of  the  heart.  The  heart  of  the  amateur  athlete, 
bicyclist,  or  mountain  climber  is  frequently  injured  by 
attempting  more  than  the  previous  training  warrants. 
The  new  work  should  be  taken  up  gradually,  and  feats 
requiring  a  large  outlay  of  physical  energy  should  be  at- 
tempted only  after  long  periods  of  training. 

Since  the  heart  is  controlled  by  the  nervous  system,  it 
frequently  becomes  irregular  in  its  action  through  condi- 
tions that  exhaust  the  nervous  energy.  Palpitations  of  the 
heart,  the  missing  of  beats,  and  pains  in  the  heart  region 
frequently  arise  from  this  cause.  It  is  through  their  effect 
upon  the  nervous  system  that  worry,  overstudy,  undue 
excitement,  and  dissipation  cause  disturbances  of  the  heart. 
In  all  such  cases  the  remedy  lies  in  the  removal  of  the 
cause.  The  nervous  system  should  also  be  "  toned  up  " 
through  rest,  plenty  of  sleep,  and  moderate  exercise  in  the 
open  air. 

Effect  of  Drugs.  —  A  number  of  substances  classed  as 
drugs,  mainly  by  their  action  on  the  nervous  system,  pro- 

1  Active  exercise  through  short  intervals,  followed  by  periods  of  rest,  such  as  the 
exercise  furnished  by  climbing  stairs,  or  by  short  runs,  is  considered  the  best  means 
of  strengthening  the  heart. 


0  THE   VITAL   PROCESSES 

duce  undesirable  effects  upon  the  organs  of  circulation. 
Unfortunately  some  of  these  are  extensively  used,  alcohol 
being  one  of  them.  If  taken  in  any  but  small  quantities, 
alcohol  is  a  disturbing  factor  in  the  circulation.  It  in- 
creases the  rate  of  the  heart  beat  and  dilates  the  capil- 
laries. Its  effect  upon  the  capillaries  is  shown  by  the 
"  bloodshot "  eye  and  the  "  red  nose  "  of  the  hard  drinker. 
Another  bad  effect  from  the  use  of  much  alcohol  is  the 
weakening  of  the  heart  through  the  accumulation  of  fat 
around  this  organ  and  within  the  heart  muscle.  The  use 
of  alcohol  also  leads  in  many  cases  to  a  hardening  of  the 
walls  of  the  arteries,  such  as  occurs  in  old  age.  This 
effect  makes  the  use  of  alcohol  especially  dangerous  for 
those  in  advanced  years. 

Tobacco  contains  a  drug,  called  nicotine,  which  has  a 
bad  effect  upon  the  heart  in  at  least  two  ways :  I.  When 
the  use  of  tobacco  is  begun  in  early  life,  it  interferes  with 
the  growth  of  the  heart,  leading  to  its  weakness  in  the 
adult.  2.  When  used  in  considerable  quantity,  by  young 
or  old,  it  causes  a  nervous  condition  both  distressing  and 
dangerous,  known  as  "  tobacco  heart." 

Tea  and  coffee  contain  a  drug,  called  caffeine,  which  acts 
upon  the  nervous  system  and  which  may,  on  this  account, 
interfere  with  the  proper  control  of  the  heart.  In  some 
individuals  the  taking  of  a  very  small  amount  of  either 
tea  or  coffee  is  sufficient  to  cause  irregularities  in  the  action 
of  the  heart.  Tea  is  considered  the  milder  of  the  two 
liquids  and  the  one  less  liable  to  injure. 

Effect  of  Rheumatism.  —  The  disease  which  affects  the 
heart  more  frequently  than  any  other  is  rheumatism. 
This  attacks  the  lining  membrane,  or  endocardium,  and 
causes,  not  infrequently,  a  shrinkage  of  the  heart  valves. 
The  heart  is  thus  rendered  defective  and,  to  perform  its 


THE   CIRCULATION  57 

function  in  the  body,  must  work  harder  than  if  it  were  in 
a  normal  condition.  Rheumatic  attacks  of  the  heart  do 
most  harm  when  they  occur  in  early  life  —  the  period 
when  the  valves  are  the  most  easily  affected.  Any  ten- 
dency toward  rheumatism  in  children  has,  therefore,  a 
serious  significance  and  should  receive  the  attention  of  the 
physician.  Any  one  having  a  defective  heart  should  avoid 
all  forms  of  exercise  that  demand  great  exertion. 

Strengthening  of  the  Blood  Vessels.  —  Disturbances  of 
the  circulation,  causing  too  much  blood  to  be  sent  to  cer- 
tain parts  of  the  body  and  an  insufficient  amount  to  others, 
when  resulting  from  slight  causes,  are  usually  due  to  weak- 
ness of  the  walls  of  the  blood  vessels,  particularly  of  the 
muscular  coat.  Such  weakness  is  frequently  indicated  by 
extreme  sensitiveness  to  heat  or  cold  and  by  a  tendency  to 
"  catch  cold."  From  a  health  standpoint  the  preservation 
of  the  normal  muscular  "  tone  "  of  the  blood  vessels  is  a 
problem  of  great  importance.  Though  the  muscles  of  the 
blood  vessels  cannot  be  exercised  in  the  same  manner  as 
the  voluntary  muscles,  they  may  be  called  actively  into 
play  through  all  the  conditions  that  induce  changes  in  the 
blood  supply  to  different  parts  of  the  body.  The  usual 
forms  of  physical  exercise  necessitate  such  changes  and 
indirectly  exercise  the  muscular  coat.  The  exposure  of 
the  body  to  cold  for  short  intervals,  because  of  the  changes 
in  the  circulation  which  this  induces,  also  serves  the  same 
purpose.  A  cold  bath  taken  with  proper  precautions  is 
beneficial  to  the  circulation  of  many  and  so  also  is  a  brisk 
walk  on  a  frosty  morning.  Both  indirectly  exercise  and 
strengthen  the  muscular  coat  of  the  blood  vessels.  On 
the  other  hand,  too  much  time  spent  indoors,  especially  in 
overheated  rooms,  leads  to  a  weakening  of  the  muscular 
coat  and  should  be  avoided. 


58  THE   VITAL   PROCESSES 

Checking  of  Flow  of  Blood  from  Wounds.  —  The  loss  of 
any  considerable  quantity  of  blood  is  such  a  serious  matter 
that  every  one  should  know  the  simpler  methods  of  check- 
ing its  flow  from  wounds.  In  small  wounds  the  flow  is 
easily  checked  by  binding  cotton  or  linen  fiber  over  the 
place.  The  absorbent  cotton,  sold  in  small  packages  at 
drug  stores,  is  excellent  for  this  purpose  and  should  be 
kept  in  every  home.  A  simple  method  of  checking  "  nose- 
bleed "  is  that  of  drawing  air  through  the  bleeding  nostril, 
while  the  other  nostril  is  compressed  with  the  finger.1 
Another  method  is  to  "  press  with  the  finger  (or  insert  a 
small  roll  of  paper)  under  the  lip  against  the  base  of  the 
nose."  2  Where  the  bleeding  is  persistent,  the  nostril  should 
be  plugged  with  a  small  roll  of  clean  cotton  or  paper. 
When  this  is  done,  the  plug  should  not  be  removed  too 
soon  because  of  the  likelihood  of  starting  the  flow  afresh. 

In  dealing  with  large  wounds  the  services  of  a  physician 
are  indispensable.  But  in  waiting  for  the  physician  to  arrive 
temporary  aid  must  be  rendered.  The  one  who  gives 
such  aid  should  first  decide  whether  an  artery  or  a  vein  has 
been  injured.  This  is  easily  determined  by  the  nature  of 
the  blood  stream,  which  is  in  jets,  or  spurts,  from  an  artery, 
but  flows  steadily  from  a  vein.  If  an  artery  is  injured,  the 
limb  should  be  tightly  bandaged  on  the  side  of  the  wound 
nearest  the  heart ;  if  a  vein,  on  the  side  farthest  from  the 
heart.  In  addition  to  this,  the  edges  of  the  wound  should 
be  closed  and  covered  with  cotton  fiber  and  the  limb 
should  be  placed  on  a  support  above  the  level  of  the  rest 
of  the  body.  A  large  handkerchief  makes  a  convenient 
bandage  if  properly  applied.  This  should  be  folded  diag- 

1  Nosebleed   in  connection  with  any  kind  of  severe  sickness   should    receive 
prompt  attention,  since  a  considerable  loss  of  blood  when  the  body  is  already  weak 
may  seriously  delay  recovery. 

2  Newton,  Practical  Hygiene. 


THE    CIRCULATION  59 

onally  and  a  knot  tied  in  the  middle.  Opposite  ends  are 
then  tied,  making  a  loose-fitting  loop  around  the  limb. 
The  knot  is  placed  directly  over  the  blood  vessel  to  be 
compressed  and  a  short  stick  inserted  in  the  loop.  The 
necessary  pressure  is  then  applied  by  twisting  the  hand- 
kerchief with  the  stick.  Time  must  not  be  lost,  however, 
in  the  preparation  of  a  suitable  bandage.  The  blood 
vessel  should  be  compressed  with  the  fingers  while  the 
bandage  is  being  prepared. 

Summary.  —  The  blood,  to  serve  as  a  transporting  agent, 
must  be  kept  continually  moving  through  all  parts  of  the 
body.  The  blood  vessels  hold  the  blood,  supply  the  chan- 
nels and  force  necessary  for  its  circulation,  and  provide  con- 
ditions which  enable  materials  both  to  enter  and  to  leave 
the  blood  stream.  The  heart  is  the  chief  factor  in  propel- 
ling the  blood,  although  the  muscles  and  the  elastic  tissue 
in  the  walls  of  the  arteries  and  the  valves  in  the  veins  are 
necessary  aids  in  the  process.  In  the  capillaries  the  blood 
takes  on  and  gives  off  materials,  while  the  arteries  and 
veins  serve  chiefly  as  tubes  for  conveying  the  blood  from 
one  system  of  capillaries  to  another. 

Exercises.  —  i.  Of  what  special  value  in  the  study  of  the  body  was 
the  discovery  of  the  circulation  of  the  blood? 

2.  State  the  necessity  for  a  circulating  liquid  in  the  body. 

3.  Show  by  a  drawing  the  general  plan  of  the  heart,  locating  and 
naming  the  essential    parts.     Show  also  the  connection  of  the  large 
blood  vessels  with  the  cavities  of  the  heart. 

4.  Compare  the  purpose  served  by  the  chordae  tendineae  to  that 
served   by   doorstops    (the   strips   against  which   the   door  strikes  in 
closing). 

5.  Explain   how   the   heart   propels   the  blood.     To  what  class  of 
pumps  does   it  belong?     What   special    work   is   performed   by   each 
of  its  divisions? 

6.  Define  a  valve.     Of  what  use  are  the  valves  in  the  heart?     In 
the  veins? 


6o 


THE   VITAL   PROCESSES 


7.  By  what  means  is  pressure  from  contracting  muscles  in  different 
parts  of  the  body  made  to  assist  in  the  circulation  ? 

8.  Of  what  advantage  is  the  elasticity  of  the  arteries? 

9.  How  is  blood  forced  from  the  capillaries  back  to  the  heart? 

10.  Why  should  there  be  a  difference  in  structure  between  the  two 
sides  of  the  heart  ? 

11.  Following  Fig.  23,  trace  the  blood  through  a  complete  circula- 
tion, naming  all  the  divisions  of  the  system  in  the  order  of  the  flow  of 
the  blood. 

12.  If  the  period  of  rest  following  the  period  of  contraction  of  the 
heart  be  as  long  as  the  period  of  contraction,  how  many  hours  is  the 
heart  able  to  rest  out  of  every  twenty-four? 

13.  State  the  functions  of  the  capillaries.     Show  how  their  structure 
adapts  them  to  their  work. 

14.  What  kind  of  physical  exercise  tends  to  strengthen  the  heart? 
What  forms  of  exercise  tend  to  injure  it?     State  the  effects  of  alcohol 
and  tobacco  on  the  heart. 

15.  How  may  rheumatism  injure  the  heart? 

1 6.  Give  directions  for  checking  the  flow  of  blood  from  small  and 
from  large  blood  vessels. 

PRACTICAL  WORK 

In  showing  the  relations  of  the  different  parts  of  the  heart,  a  large 
dissectible  model  is  of  great  service  (Fig.  24).  Indeed,  where  the  time 
of  the  class  is  limited,  the  practical  work  may  be  confined  to  the  study 
of  the  heart  model,  diagrams  of  the  heart  and  the  circulation,  and  a  few 
simple  experiments.  However,  where  the  course  is  more  extended,  the 
dissection  of  the  heart  of  some  animal  as  described  below  is  strongly 
advised. 

Observations  on  the  Heart.  —  Procure,  by  the  assistance  of  a  butcher, 
the  heart  of  a  sheep,  calf,  or  hog.  To  insure  the  specimen  against 
mutilation,  the  lungs  and  the  diaphragm  must  be  left  attached  to  the 
heart.  In  studying  the  different  parts,  good  results  will  be  obtained  by 
observing  the  following  order : 

1.  Observe  the  connection  of  the  heart  to  the  lungs,  diaphragm, 
and  large  blood  vessels.     Inflate  the  lungs  and  observe  the  position  of 
the  heart  with  reference  to  them. 

2.  Examine  the  sac  surrounding  the  heart,  called  the  pericardium. 
Pierce  its  lower  portion  and  collect  the  pericardial  fluid.     Increase  the 


THE    CIRCULATION 


61 


opening  thus  made  until  it  is  large  enough  to  slip  the  heart  out  through 
it.     Then  slide  back  the  pericardium  until  its  connection  with  the  large 
blood  vessels  above  the  heart  is  found. 
Observe  that  a  thin  layer  of  it  continues 
down  from  this  attachment,  forming  the 
outer  covering  of  the  heart. 

3.  Trace   out   for  a   short    distance 
and  study  the  veins  and  arteries  con- 
nected with   the   heart.      The  arteries 
are  to  be  distinguished  by  their  thick 
walls.     The  heart  may  now  be  severed 
from    the   lungs   by    cutting   the   large 
blood  vessels,  care  being  taken  to  leave 
a    considerable    length    of    each     one 
attached  to  the  heart. 

4.  Observe  the  outside  of  the  heart. 
The  thick,  lower  portion  contains  the 
cavities    called    "ventricles ;     the    thin, 
upper,  ear-shaped  portions  are  the  auri- 
cles.    The  thicker  and  denser  side  lies 
toward  the  left  of  the  animal's  body  and 

is  called  the  left  side  of  the  heart ;  the  other  is  the  right  side.  Locate 
the  right  auricle  and  the  right  ventricle ;  the  left  auricle  and  the  left 
ventricle. 

5.  Lay  the  heart  on  the  table  with  the  front  side  up  and  the  apex 
pointing  from  the  operator.     This  places  the  left  side  of  the  heart  to 
his  left  and  the  right  side  to  his  right.     Notice  the  groove  between  the 
ventricles,  called  the  inter-ventricular  groove.    Make  an  incision  half  an 
inch  to  the  right  of  this  groove  and  cut  toward  the  base  of  the  heart 
until  the  pulmonary  artery  is  laid  open.     Then,  following  within  half  an 
inch  of  the  groove,  cut  down  and  around  the  right  side  of  the  heart. 
The  wall  of  the  right  ventricle  may  now  be  raised  and  the  cavity  ex- 
posed.    Observe   the   extent   of  the  cavity,  its   shape,  its   lining,  its 
columns  of  muscles,  its  half  columns  of  muscles,  its  tendons  (chordae 
tendineae),  the  tricuspid  valve  from  the  under  side,  etc.    Also  notice  the 
valve  at  the  beginning  of  the  pulmonary  artery  (the  right  semilunar) 
and  the  sinuses,  or  depressions,  in  the  artery  immediately  behind  its 
divisions. 

6     Now  cut  through  the  middle  of  the  loosened  ventricular  wall  from 
the  apex  to  the  middle  of  the  right  auricle,  laying  it  open  for  observa- 


FIG.  24.  —  Model  for  demon- 
strating the  heart. 


62  THE   VITAL   PROCESSES 

tion.  Observe  the  openings  into  the  auricle,  there  being  one  each  for 
the  vena  cava  superior,  the  vena  cava  inferior,  and  the  coronary  vein. 
Compare  the  walls,  lining,  shape,  size,  etc.,  with  the  ventricle  below. 

7.  Cut  off  the  end  of  the  left  ventricle  about  an  inch  above  the  apex. 
This  will  show  the  extension  of  the  cavity  to  the  apex ;   it  will  also 
show  the  thickness  of  the  walls  and  the  shape  of  the  cavity.     Split  up 
the  ventricular  wall  far  enough  to  examine  the  mitral  valve  and  the 
chordae  tendineae  from  the  lower  side. 

8.  Make  an  incision  in  the  left  auricle.     Examine  its  inner  surface 
and  find  the  places  of  entrance  of  the  pulmonary  veins.     Examine  the 
mitral  valve  from  above.     Compare  the  two  sides  of  the  heart,  part 
for  part. 

9.  Separate  the  aorta  from  the  other  blood  vessels  and  cut  it  entirely 
free  from  the  heart,  care  being  taken  to  leave  enough  of  the  heart  at- 
tached to  the  artery  to  insure  the  semilunar  valve's  being  left  in  good 
condition.     After  tying  or  plugging  up  the  holes  in  the  sides  of  the 
artery,  pour  water  into  the  small  end  and  observe  the  closing  of  the 
semilunar  valve.     Repeat  the  experiment  until  the  action  of  the  valve  is 
understood.    Sketch  the  artery,  showing  the  valve  in  a  closed  condition. 

To  illustrate  the  Action  of  a  Ventricle.  —  Procure  a  syringe  bulb  with 
an  opening  at  each  end.  Connect  a  rubber  tube  with  each  opening, 
letting  the  tubes  reach  into  two  tumblers  containing  water.  By  alter- 
nately compressing  and  releasing  the  bulb,  water  is  pumped  from  one 
vessel  into  the  other.  The  bulb  may  be  taken  to  represent  one  of  the 

ventricles.  What  action  of  the 
ventricle  is  represented  by  com- 
pressing the  bulb  ?  By  releasing 
the  pressure  ?  Show  by  a  sectional 
drawing  the  arrangement  of  the 
valves  in  the  syringe  bulb. 

To  show  the  Advantage  of  the 
FIG.  25.  -  Illustrating  elasticity  of     Elasticity  of  Arteries.  —  Connect 
arteries.  tne  syringe  bulb  used  in  the  last 

experiment    with    a    rubber    tube 

three  or  four  feet  in  length  and  having  rather  thin  walls.  In  the  oppo- 
site end  of  the  rubber  tube  insert  a  short  glass  tube  which  has  been 
drawn  (by  heating)  to  a  fine  point  (Fig.  25).  Pump  water  into  the 
rubber  tube,  observing : 

i.  The  swelling  of  the  tube  (pulse)  as  the  water  is  forced  into  it. 
(This  is  best  observed  by  placing  the  fingers  on  the  tube.) 


THE    CIRCULATION  63 

2.  The  forcing  of  water  from  the  pointed  tubs  during  the  interval 
when  no  pressure  is  being  applied  from  the  bulb.  Compare  with  the 
action  of  the  arteries  when  blood  is  forced  into  them  from  the 
ventricles. 

Repeat  the  experiment,  using  a  long  glass  tube  terminating  in  a  point 
instead  of  the  rubber  tube.  (In  fitting  the  glass  tube  to  the  bulb  use 
a  very  short  rubber  tube.)  Observe  and  account  for  the  differences  in 
the  flow  of  water  through  the  inelastic  tube. 

To  show  the  Advantage  of  Valves  in  the  Veins.  —  Attach  an  open 
glass  tube  one  foot  in  length  to  each  end  of  the  rubber  tube  used  in  the 
preceding  experiment  and  fill  with  water 
(by  sucking)  to  within  about  six  inches  of 
the  end.  Lay  on  the  table  with  the  glass 
tubes  secured  in  an  upright  position  (Fig. 
26).  Now  compress  the  tube  with  the 
hand,  noting  that  the  water  rises  in  both  /IG;  26--~  Simple  appa- 

ratus  for  showing  advantage 
tubes,  being   pushed    in  both   directions.     of  vaives  in  veins. 

This  effect  is  similar  to  that  produced  on 

the  blood  when  a  vein  having  no  valves  is  compressed. 

Now  imitate  the  action  of  a  valve  by  clamping  the  tube  at  one  point, 
or  by  closing  it  by  pressure  from  the  finger,  and  then  compressing  with 
the  hand  some  portion  of  the  tube  on  the  table.  Observe  in  this  in- 
stance that  the  water  is  all  pushed  in  the  same  direction.  The  move- 
ment of  the  water  is  now  like  the  effect  produced  on  the  blood  in  veins 
having  valves  when  the  veins  are  compressed. 

To  show  the  Position  of  the  Valves  in  the  Veins.  —  Exercise  the  arm 
and  hand  for  a  moment  to  increase  the  blood  supply.  Expose  the  fore- 
arm and  examine  the  veins  on  its  surface.  With  a  finger,  stroke  one  of 
the  veins  toward  the  heart,  noting  that,  as  the  blood  is  pushed  along 
on  one  side  of  the  finger  the  blood  follows  on  the  other  side.  Now  stroke 
the  vein  toward  the  hand.  Places  are  found  beyond  which  the  blood 
does  not  follow  the  finger.  These  mark  the  positions  of  valves. 

To  show  Effect  of  Exercise  upon  the  Circulation.  —  i .  With  a  finger 
on  the  "  pulse  "  at  the  wrist  or  temple,  count  the  number  of  heart  beats 
during  a  period  of  one  minute  under  the  following  conditions :  (#) 
when  sitting ;  (6)  when  standing ;  (c)  after  active  exercise,  as  run- 
ning. What  relation,  if  any,  do  these  observations  indicate  between 
the  general  activity  of  the  body  and  the  work  of  the  heart? ' 

2.  Compare  the  size  of  the  veins  on  the  backs  of  the  hands  when 
they  are  placed  side  by  side  on  a  table.  Then  exercise  briskly  the 


64  THE   VITAL   PROCESSES 

right  hand  and  arm,  clenching  and  unclenching  the  fist  and  flexing  the 
arm  at  the  elbow.  Place  the  hands  again  side  by  side  and,  after  wait- 
ing a  minute,  observe  the  increase  in  the  size  of  the  veins  in  the 
hand  exercised.  How  is  this  accounted  for  ? 

To  show  the  Effect  of  Gravity  on  the  Circulation.  —  Hold  one  hand 
high  above  the  head,  at  the  same  time  letting  the  other  hand  hang 
loosely  by  the  side.  Observe  the  difference  in  the  color  of  the  hands 
and  the  degree  to  which  the  large  veins  are  filled.  Repeat  the  experi- 
ment, reversing  the  position  of  the  hands.  What  results  are  observed? 
In  what  parts  of  the  body  does  gravity  aid  in  the  return  of  the  blood  to 
the  heart?  In  what  parts  does  it  hinder?  Where  fainting  is  caused  by 
lack  of  blood  in  the  brain  (the  usual  cause),  is  it  better  to  let  the  patient 
lie  down  flat  or  to  force  him  into  a  sitting  posture? 

To  study  the  Circulation  in  a  Frog's  Foot  (Optional).  —  A  com- 
pound microscope  is  needed  in  this  study  and  for  extended  examination 
it  is  best  to  destroy  the  frog's  brain.  This  is  done  by  inserting  some 
blunt-pointed  instrument  into  the  skull  cavity  from  the  neck  and  moving 
it  about.  A  small  frog,  on  account  of  the  thinness  of  its  webs,  gives  the 
best  results.  It  should  be  attached  to  a  thin  board  which  has  an  open- 
ing in  one  end  over  which  the  web  of  the  foot  may  be  stretched. 
Threads  should  extend  from  two  of  the  toes  to  pins  driven  into  the 
board  to  secure  the  necessary  tension  of  the  web,  and  the  foot  and 
lower  leg  should  be  kept  moist.  Using  a  two-thirds-inch  objective, 
observe  the  branching  of  the  small  arteries  into  the  capillaries  and  the' 
union  of  the  capillaries  to  form  the  small  veins.  The  appearance  is 
truly  wonderful,  but  allowance  must  be  made  for  the  fact  that  the 
motion  of  the  blood  is  magnified,  as  well  as  the  different  structures,  and 
that  it  appears  to  move  much  faster  than  it  really  does.  With  a  still 
higher  power,  the  movements  of  the  corpuscles  through  the  capillaries 
may  be  studied. 

NOTE.  —  To  perform  this  experiment  without  destroying  the  brain, 
the  frog  is  first  carefully  wrapped  with  strips  of  wet  cloth  and  securely 
tied  to  the  board.  The  wrapping,  while  preventing  movements  of  the 
frog,  must  not  interfere  with  the  circulation. 


CHAPTER  VI 


THE  LYMPH  AND  ITS  MOVEMENT  THROUGH  THE  BODY 

THE  blood,  it  will  be  remembered,  moves  everywhere 
through  the  body  in  a  system  of  closed  tubes.  These  keep 
it  from  coming  in  contact  with 
any  of  the  cells  of  the  body  except 
those  lining  the  tubes  themselves. 
The  capillaries,  to  be  sure,  bring 
the  blood  very  near  the  cells  of 
the  different  tissues ;  still,  there 
is  need  of  a  liquid  to  fill  the  space 
between  the  capillaries  and  the 
cells  and  to  transfer  materials 
from  one  to  the  other.  The 
lymph  occupies  this  position  and 
does  this  work.  The  position  of 
the  lymph  with  reference  to  the 
capillaries  and  the  cells  is  shown 
in  Fig.  27. 

Origin  of  the  Lymph. — The 
chief  source  of  the  lymph  is  the 
plasma  of  the  blood.  As  before 
described,  the  walls  of  the  capillaries  consist  of  a  single 
layer  of  flat  cells  placed  edge  to  edge.  Partly  on  account 
of  the  pressure  upon  the  blood  and  partly  on  account  of  the 
natural  tendency  of  liquids  to  pass  through  animal  mem- 
branes, a  considerable  portion  of  the  plasma  penetrates  the 
thin  walls  and  enters  the  spaces  occupied  by  the  lymph. 

65 


FIG.  27.  —  Diagram  show- 
ing position  of  the  lymph 
with  reference  to  the  blood 
and  the  cells.  The  central 
tube  is  a  capillary.  The  arrows 
indicate  the  direction  of  slight 
movements  in  the  lymph. 


66  THE   VITAL   PROCESSES 

The  cells  themselves  also  help  to  form  the  lymph,  since 
the  water  and  wastes  leaving  the  cells  add  to  its  bulk. 
These  mix  with  the  plasma  from  the  blood,  forming  the 
resultant  liquid  which  is  the  lymph.  A  considerable 
amount  of  the  material  absorbed  from  the  food  canal  also 
enters  the  lymph  tubes,  but  this  passes  into  the  blood 
before  reaching  the  cells. 

Composition  and  Physical  Properties  of  the  Lymph.1 — As 
would  naturally  be  expected,  the  composition  of  the  lymph 
is  similar  to  that  of  the  blood.  In  fact,  nearly  all  the 
important  constituents  of  the  blood  are  found  in  the  lymph, 
but  in  different  proportions.  Food  materials  for  the  ceils 
are  present  in  smaller  amounts  than  in  the  blood,  while  im- 
purities from  the  cells  are  in  larger  amounts.  As  a  rule 
the  red  corpuscles  are  absent  from  the  lymph,  but  the 
white  corpuscles  are  present  and  in  about  the  same  num- 
bers as  in  the  blood. 

The  physical  properties  of  the  lymph  are  also  similar  to 
those  of  the  blood.  Like  the  blood,  the  lymph  is  denser 
than  water  and  also  coagulates,  but  it  coagulates  more 
slowly  than  does  the  blood.  The  most  noticeable  differ- 
ence between  these  liquids  is  that  of  color,  the  lymph  being 
colorless.  This  is  due  to  the  absence  of  red  corpuscles. 
The  quantity  of  lymph  is  estimated  to  be  considerably 
greater  than  that  of  the  blood. 

Lymph  Vessels.  —  Most  of  the  lymph  lies  in  minute  cav- 
ities surrounding  the  cells  and  in  close  relations  with  the 
capillaries  (Figs.  27  and  30).  These  are  called  lymph 
spaces.  Connecting  with  the  lymph  spaces  on  the  one 

1  On  account  of  its  position  in  the  body,  the  lymph  is  not  easily  collected  for 
examination.  Still,  nearly  every  one  will  recall  some  experience  that  has  enabled 
him  to  see  lymph.  The  liquid  in  a  water  blister  is  lymph,  and  so  also  is  the  liquid 
which  oozes  from  the  skin  when  it  is  scraped  or  slightly  scratched.  Swelling  in 
any  part  of  the  body  is  due  to  the  accumulation  of  lymph  at  that  place. 


THE   LYMPH   AND   ITS   MOVEMENT 


hand,  and  with  certain  blood  vessels  on  the  other,  is  a 
system  of  tubes  that  return  the  lymph  to  the  blood  stream. 
The  smallest  of  these,  and  the  ones  in  greatest  abundance, 
are  called  lymphatics. 
They  consist  of  slender, 
thin-walled  tubes,  which  re- 
semble veins  in  structure, 
and,  like  the  veins,  have 
valves.  They  differ  from 
veins,  however,  in  being 
more  uniform  in  size  and 
in  having  thinner  walls. 

The  lymphatics  in  differ- 
ent places  gradually  con- 
verge toward,  and  empty 
into,  the  two  main  lymph 
tubes  of  the  body.  The 
smaller  of  these  tubes, 
called  the  right  lymphatic 
duct,  receives  the  lymph 
from  the  lymphatics  in  the 
right  arm,  the  right  side  of 
the  head,  and  the  region 
of  the  right  shoulder.  It 
connects  with,  and  empties 
its  contents  into,  the  right 
subclavian  vein  at  the  place 
where  it  is  joined  by  the  FIG.  28.  —  Diagram  of  drainage  sys- 
.  ,  .  .  ,  .  /T^.  ox  tern  for  the  lymph,  i.  Thoracic  duct. 

right  jugular  vein  (Fig.  28).   2  Right  lymptfatic  duct.    3.  Left  sub- 

The  larger  of  the  lymph    clavian  vein.     4.  Right  subclavian  vein. 

tubes  is  called  the  thoracic  5-  SuPerior  vena  cava-     6-  Lacteals. 

.  7.  Lymphatic  glands.     The  small  tubes 

duct.       This  receives  lymph    connecting  with  the  lymph  spaces  in  all 
from  all  parts  of    the  body    parts  of  the  body  are  the  lymphatics. 


68  THE   VITAL   PROCESSES 

not  drained  by  the  right  lymphatic  duct,  and  empties  it 
into  the  left  subclavian  vein.  Connection  is  made  with  the 
subclavian  vein  on  the  upper  side  at  the  place  where  it 
is  joined  by  the  left  jugular  vein.  The  thoracic  duct  has 
a  length  of  from  sixteen  to  eighteen  inches,  and  is  about 
as  large  around  as  a  goose  quill.  The  lower  end  terminates 
in  an  enlargement  in  the  abdominal  cavity,  called  the  re- 
ceptacle of  the  chyle.  It  is  provided  with  valves  through- 
out its  course,  in  addition  to  one  of  considerable  size  which 
guards  the  opening  into  the  blood  vessel. 

The  lymphatics  which  join  the  thoracic  duct  from  the 
small  intestine  are  called  the  lacteals  (Fig.  28).  These  do 
not  differ  in  structure  from  the  lymphatics  in  other  parts  of 
the  body,  but  they  perform  a  special  work  in  absorbing  the 
digested  fat  (Chapter  XI). 

Lymphatic  Glands.  —  The  lymphatic  glands,  sometimes 
called  lymph  nodes,  are  small  and  somewhat  rounded 
bodies  situated  along  the  course  of  the  lymphatic  tubes. 
They  vary  in  size,  some  of  them  being  an  inch  or  more  in 
length.  The  lymph  vessels  generally  open  into  them  on 
one  side  and  leave  them  on  the  other  (Figs.  28  and  30). 
They  are  not  glands  in  function,  but  are  so  called  because 
of  their  having  the  general  form  of  glands.  They  provide 
favorable  conditions  for  the  development  of  white  corpus- 
cles (page  29).  They  also  separate  harmful  germs  and 
poisonous  wastes  from  the  lymph,  thereby  preventing  their 
entrance  into  the  blood. 

Relations  of  the  Lymph,  the  Blood,  and  the  Cells.  - 
While  the  blood  is  necessary  as  a  carrying,  or  transporting, 
agent  in  the  body,  the  lymph  is  necessary  for  transferring 
materials  from  the  blood  to  the  cells  and  vice  versa. 
Serving  as  a  physiological  "go  between,"  or  medium  of 
exchange,  the  lymph  enables  the  blood  to  minister  to  the 


THE   LYMPH   AND    ITS    MOVEMENT  69 

needs  of  the  cells.  But  the  lymph  and  the  blood,  every- 
thing considered,  can  hardly  be  looked  upon  as  two  sepa- 
rate and  distinct  liquids.  Not  only  do  they  supplement 
each  other  in  their  work  and  possess  striking  similarities, 
but  each  is  made  in  its  movements  to  pass  into  the  vessels 
occupied  by  the  other,  so  that  they  are  constantly  mixing 
and  mingling.  For  these  and  other  reasons,  they  are  more 
properly  regarded  as  two  divisions  of  a  single  liquid  —  one 
which,  by  adapting  itself  to  different  purposes,1  supplies 
all  the  conditions  of  a  nutrient  fluid  for  the  cells. 

Movements  of  the  Lymph.  —  As  compared  with  the 
blood,  the  lymph  must  be  classed  as  a  quiet  liquid.  But,  as 
already  suggested,  it  has  certain  movements  which  are  nec- 
essary to  the  purposes  which  it  serves.  A  careful  study 
shows  it  to  have  three  well-defined  movements  as  follows: 

1.  A  movement  from  the  capillaries  toward  the  cells. 

2.  A  movement  from  the  cells  toward  the  capillaries. 

3.  A  movement  of  the  entire  body  of  lymph  from  the 
lymph  spaces  into  the  lymphatics  and  along  these  chan- 
nels to  the  ducts  through  which  it  enters  the  blood. 

By  the  first  movement  the  cells  receive  their  nourish- 
ment. By  the  second  and  third  movements  the  lymph, 
more  or  less  laden  with  impurities,  is  returned  to  the 
blood  stream.  (See  Figs.  28  and  30.) 

Causes  of  the  Lymph  Movements.  — Let  us  consider  first 
the  movement  through  the  lymph  tubes.  No  pump,  like 
the  heart,  is  known  to  be  connected  with  these  tubes  and 

1  In  certain  small  animals  of  the  lowest  types  a  single  liquid,  serving  as  a 
medium  of  exchange  between  the  cells  and  the  body  surface,  supplies  all  the  needs 
of  the  organism.  In  larger  animals,  however,  where  materials  have  to  be  moved 
from  one  part  of  the  cell  group  to  another,  a  portion  of  the  nutrient  fluid  is  used 
for  purposes  of  transportation.  This  is  confined  in  channels  where  it  is  set  in 
motion  by  suitable  organs.  The  portion  which  remains  outside  of  the  channels 
then  transfers  material  between  the  cells,  on  the  one  hand,  and  the  moving  liquid, 
on  the  other. 


70  THE    VITAL    PROCESSES 

to  supply  the  pressure  necessary  for  moving  the  lymph. 
There  are,  however,  several  forces  that  indirectly  aid  in  its 
flow.  The  most  important  of  these  are  as  follows: 

1.  Blood  Pressure   at    the   Capillaries. — The    plasma 
which  is  forced  through  the  capillary  walls  by  pressure 
from  the  heart  makes  room  for  itself  by  pushing  a  portion 
of  the  lymph  out  of  the   lymph    spaces.      This  in  turn 
presses  upon  the  lymph  in  the  tubes  which  it  enters.     In 
this  way  pressure   from  the  heart  is  transmitted  to  the 
lymph,  forcing  it  to  move. 

2.  Variable  Pressure  on   the  Walls  of  the  Lymph   Ves- 
sels.—  Pressure  exerted  on  the  sides  of  the  lymph  tubes  by 

contracting  muscles  tends  to  close  them 
up  and  to  push   the  lymph  past  the 
valves,  which,  by  closing,  prevent  its 
return  (Fig.  29).     Pressure  at  the  sur- 
face of  the  body,  provided  that  it  is 
variable,  also  forces  the  lymph  along. 
The  valves  in  the  lymph  vessels  serve 
1 A          |L1  f  B     the  same  purpose  as  those  in  the  veins. 
FIG.   29.- Diagram        ^     Thg    Inspiratory    /w^,_Wheri 
to  show  how  the  muscles      ,        ,  .  .       .          .  ,  .      , 

pump  lymph.     A.  Re-  the  thoracic  cavlty ls  enlarged  in  breath- 

laxed     muscle     beside  ing,  the  unbalanced  atmospheric  pres- 

which   is    a  lymphatic  sure    is    exerted    from    all   directions 

tube    A  Same  muscle  towards  the  thoracic  space.     This  not 

in  state  of  contraction. 

only  causes  the  air  to  flow  into  the  lungs 
(Chapter  VII),  but  also  causes  a  movement  of  the  blood 
and  lymph  in  such  of  their  tubes  as  enter  this  cavity.  It 
will  be  noted  that  both  of  the  large  lymph  ducts  terminate 
where  their  contents  may  be  influenced  by  the  respiratory 
movements.  (See  Practical  Work.) 

Where  the  Lymph  enters  the  Blood.  —  The  fact  that  the  lymph  is 
poured  into  the  blood  at  but  two  places,  and  these  very  close  to  each 


Lymph 


THE    LYMPH    AND    ITS   MOVEMENT  71 

other,  requires  a  word  of  explanation.  As  a  matter  of  fact,  it  is  im- 
possible for  the  lymph  to  flow  into  blood  vessels  at  most  places  on 
account  of  the  blood  pressure.  This  would 
force  the  blood  into  the  lymph  vessels, 
instead  of  allowing  the  lymph  to  enter  the 
blood.  The  lymph  can  enter  only  at  some 
place  where  the  blood  pressure  is  less  than 
the  pressure  that  moves  the  lymph.  Such 
a  place  is  found  in  the  thoracic  cavity.  As 
already  pointed  out  (page  54),  the  blood 
pressure  in  the  veins  entering  this  cavity 
becomes,  with  each  expansion  of  the  chest, 
negative,  i.e.,  less  than  the  pressure  of  the 
atmosphere  on  the  outside  of  the  body. 
This,  as  we  have  seen,  aids  in  the  flow 
of  the  blood  into  the  right  auricle.  It  also 
'Gland  aids  in  the  passage  of  lymph  into  the 
blood  vessels.  The  lymph  is  said  to  be 
"  sucked  in,"  which  means  that  it  is  forced 
in  by  the  unbalanced  pressure  of  the 
atmosphere.1  Some  advantage  is  also 
gained  by  the  lymph 
duct's  entering  the 
Capillary  subclavian  vein  on 
the  upper  side  and 
at  its  union  with  the 
jugular  vein.  Every- 

FIG.  30.  —  Diagram  showing  gen-  thing  considered,  it 

eral  movement  of  lymph  from  the  place        SSjSgljX        [s    found    that    the 
of  relatively  high  pressure  at  the  lymph       S~  lymph     flows     into 

spaces  to  the  place  of  relatively  low      T  the     blood    vessels 

pressure  in  the  thoracic  cavity.  where     jt    can     be 

"  drawn  in  "  by  the  movements  of  breathing  and  where  it  meets  with  no 
opposition  from  the  blood  stream  itself  (Fig.  30). 

Lymph  Movements  at   the    Cells.  —  The   double   move- 
ment of  the  lymph  from  the  capillaries  toward  the  cells 


Lymphatic 
lube 


1  Surgeons  in  opening  veins  near  the  thoracic  cavity  have  to  be  on  their  guard  to 
prevent  air  from  being  sucked  into  them,  thereby  causing  death. 


72  THE   VITAL    PROCESSES 

and  from  the  cells  toward  the  capillaries  is  not  entirely 
understood.  Blood  pressure  in  the  capillaries  undoubtedly 
has  much  to  do  in  forcing  the  plasma  through  the  capil- 
lary walls,  but  this  tends  to  prevent  the  movement  of  the 
lymph  in  the  opposite  direction.  Movements  between  the 
blood  and  the  lymph  are  known  to  take  place  in  part 
according  to  a  general  principle,  known  as  osmosis,  or 
dialysis. 

Osmosis.  —  The  term  "  osmosis  "  is  used  to  designate  the  passage  of 
liquids  through  some  partition  which  separates  them.     Thus,  if  a  vessel 

with  an  upright  membranous  partition 
be  filled  on  the  one  side  with  pure 
water  and  on  the  other  with  water  con- 
taining salt,  an  exchange  of  materials 
will  take  place  through  the  membrane 
until  the  same  proportion  of  salt  exists 


FIG.  31.-  Vessel  with  an  on  the  two  sides  (Fig.  31).  The  cause 
upright  membranous  partition  for  rf  ^^  .g  ^  ^.^  rf  ^  ^^ 

illustrating  osmosis.  .  .  .       x,    A        . 

cules,  or  minute  particles,  that  make  up 

the  liquid  substance.     If  the  partition  were  not  present,  this  motion 
would  simply  cause  a  mixing  of  the  liquids. 

Conditions  under  which  Osmosis  occurs.  —  Osmosis  may  be  shown  by 
suitable  experiments  (see  Practical  Work)  to  take  place  under  the  fol- 
lowing conditions  : 

1.  The  liquids  on  the  two  sides  of  the  partition  must  be  unlike  either 
in  density  or  in  composition.      Since  the  effect  of  the  movement  is  to 
reduce  the  liquids  to  the  same  condition,  a  difference  in  density  causes  the 
flow  to  be  greater  from  the  less  dense  toward  the  denser  liquid,  than  in 
the  opposite  direction  ;    while  a  difference  in   composition   causes  the 
substances  in  solution  to  move  from  the  place  of  greater  abundance 
toward  places  of  less  abundance. 

2.  The  liquids  must  be  capable  of  wetting,  or  penetrating,  the  par- 
tition.    If  but  one  of  the  liquids  penetrates  the  partition,  the  flow  will 
be  in  but  one  direction. 

3.  The  liquids  on  the  two  sides  of  the  partition  must  readily  mix 
with  each  other. 

Osmosis  at  the  Cells.  —  In  the  body  osmosis  takes  place  between  the 


THE    LYMPH   AND   ITS   MOVEiMENT  73 

blood  and  the  lymph  and  between  the  lymph  and  the  cells,  the  movements 
being  through  the  capillary  walls  and  the  membranes  inclosing  the  cells 
(Fig.  27).  Oxygen  and  food  materials,  which  are  found  in  great  abun- 
dance in  the  blood,  are  less  abundant  in  the  lymph  and  still  less  abun- 
dant in  the  cells.  According  to  the  principle  of  osmosis,  the  main  flow 
of  oxygen  and  food  is  from  the  capillaries  toward  the  cells.  On  the 
other  hand,  the  wastes  are  most  abundant  in  the  cells  where  they  are 
formed,  less  abundant  in  the  lymph,  and  least  abundant  in  the 
blood.  Hence  the  wastes  flow  from  the  cells  toward  the  capillaries. 

Solutions. — Neither  the  blood  plasma  nor  the  lymph,  as  already 
shown,  are  simple  liquids  ;  but  they  consist  of  water  and  different  sub- 
stances dissolved  in  the  water.  They  belong  to  a  class  of  substances 
called  solutions.  The  chief  point  of  interest  about  substances  in  solu- 
tion is  that  they  are  very  finely  divided  and  that  their  little  particles 
are  free  to  move  about  in  the  liquid  that  contains  them.  Both  the 
motion  and  the  finely  divided  condition  of  the  dissolved  substances 
are  necessary  to  the  process  of  osmosis.  All  substances,  however,  that 
appear  to  be  in  solution  are  not  able  to  penetrate  membranes,  or  take 
part  in  osmosis. 

Kinds  of  Solutions  in  the  Body. — The  substances  in  solution  in  the 
body  liquids  are  of  two  general  kinds  known  as  colloids  and  crystal- 
loids. The  crystalloids  are  able  to  pass  through  membranous  parti- 
tions, while  the  colloids  are  not.  An  example  of  a  colloid  is  found  in 
the  albumin  of  an  egg,  which  is  unable  to  penetrate  the  membrane 
which  surrounds  it.  Examples  of  crystalloids  are  found  in  solutions 
of  salt  and  sugar  in  water.  The  inability  of  a  colloid  to  penetrate  a 
membrane  is  due  to  the  fact  that  it  does  not  form  a  true  solution.  Its 
particles  (molecules),  instead  of  being  completely  separated,  still  cling 
together,  forming  little  masses  that  are  too  large  to  penetrate  the  mem- 
brane. Since,  however,  it  has  the  appearance,  on  being  mixed  with 
water,  of  being  dissolved,  it  is  called  a  colloidal  solution.  The  crystal- 
loid substance,  on  the  other  hand,  completely  separates  in  the  water 
and  forms  a  true  solution  —  one  which  is  able  to  penetrate  the  partition 
or  membrane. 

Osmosis  not  a  Sufficient  Cause.  —  The  passage  of  materials  through 
animal  membranes,  according  to  the  principle  of  osmosis,  is  limited  to 
crystalloid  substances.  But  colloid  substances  are  also  known  to  pass 
through  the  various  partitions  of  the  body.  An  example  of  such  is 
found  in  the  proteids  of  the  blood  which,  as  a  colloidal  solution,  pass 
through  the  capillary  walls  to  become  a  part  of  the  lymph.  Perhaps 


74  THE   VITAL   PROCESSES 

the  best  explanation  offered  as  yet  for  this  passage  is  that  the  colloidal 
substances  are  changed  by  the  cells  lining  the  capillaries  into  sub- 
stances that  form  true  solutions  and  that  after  the  passage  they  are 
changed  back  again  to  the  colloidal  condition. 

Summary.  —  Between  the  cells  and  the  capillaries  is  a 
liquid,  known  as  the  lymph,  which  is  similar  in  composi- 
tion and  physical  properties  to  the  blood.  It  consists 
chiefly  of  escaped  plasma.  The  vessels  that  contain  it 
are  connected  with  the  system  for  the  circulation  of  the 
blood.  By  adding  new  material  to  the  lymph  and  with- 
drawing waste  material  from  it,  the  blood  keeps  this  liquid 
in  a  suitable  condition  for  supplying  the  needs  of  the  cells. 
Supplementing  each  other  in  all  respects,  the  blood  and 
the  lymph  together  form  the  nutrient  cell  fluid  of  the 
body.  The  interchange  of  material  between  the  blood 
and  the  lymph,  and  the  lymph  and  the  cells,  takes  place 
in  part  according  to  the  principle  of  osmosis. 

Exercises.  —  I.    Explain  the  necessity  for  the  lymph  in  the  body. 

2.  Compare  lymph  and  water  with  reference  to  density,  color,  and 
complexity  of  composition. 

3.  Compare  lymph  and  blood  with  reference  to  color,  composition, 
and  movement  through  the  body. 

4.  Show  how  blood  pressure  in  the  capillaries  causes  a  flow  of  the 
lymph. 

5.  Show  how  contracting  muscles  cause  the  lymph  to  move.     Com- 
pare with  the  effect  of  muscular  contraction  upon  the  blood  in  the 
veins. 

6.  Trace  ihe  lymph  in  its  flow  from  the  right  hand  to  where  it  enters 
the  blood ;  from  the  feet  to  where  it  enters  the  blood. 

7.  What  conditions  prevail  at  the  cells  to  cause  a  movement  of  food 
and  oxygen  in  one  direction  and  of  waste  materials  in  the  opposite 
direction? 

8.  What  part  does  water  play  in  the  exchanges  at  the  cells? 

9.  Show  that  the  blood  and  the  lymph  together  fulfill  all  the  re- 
quirements of  a  nutrient  cell  fluid  in  the  body. 


THE  LYMPH  AND  ITS  MOVEMENT 


75 


PRACTICAL  WORK 

To  illustrate  the  Effect  of  Breathing  upon  the  Flow  of  Lymph. — 
Tightly  holding  one  end  of  a  glass  tube  between  the  lips,  let  the  other 
end  extend  into  water  in  a  tumbler  on  a  table.  In  this  position  quickly 
inhale  air  through  the  nostrils,  noting  that  with  each  inhalation  there  is 
a  slight  movement  of  the  water  up  the  tube.  (No  sucking  action  should 
be  exerted  by  the  mouth.)  Apply  to  the  movements  in  the  large  blood 
and  lymph  vessels  entering  the  thoracic  cavity. 

To  illustrate  Osmosis.  —  i .  Separate  the  shell  from  the  lining  mem- 
brane at  one  end  of  an  egg,  over  an  area  about  one  inch  in  diameter. 
To  do  this  without  injuring  the  membrane,  the  shell  must  first  be 
broken  into  small  pieces  and  then  picked  off  with  a  pair  of  forceps, 
or  a  small  knife  blade.  Fit  a  small  glass  tube,  eight  or  ten  inches 
long,  into  the  other  end  so  that  it  will  penetrate  the  membrane  and 
pass  down  into  the  yolk.  Securely  fasten  the  tube  to 
the  shell  by  melting  beeswax  around  it,  and  set  the  egg 
in  a  small  tumbler  partly  filled  with  water.  Examine  in 
the  course  of  half  an  hour.  What  evidence  now  exists 
that  the  water  has  passed  through  the  membrane  ? 

2.  Tie  over  the  large  end  of  a  "thistle  tube"  (used 
by  chemists)  a  thin  animal  membrane,  such  as  a  piece 
of  the  pericardium  or  a  strip  of  the  membrane  from 
around  a  sausage.  Then  fill  the  bulb  and  the  lower  end 
of  the  tube  with  a  concentrated  solution  of  some  solid, 
such  as  sugar,  salt,  or  copper  sulphate.  Suspend  in  a 
vessel  of  water  so  that  the  liquid  which  it  contains  is 
just  on  a  level  with  the  water  in  the  vessel.  Examine 
from  time  to  time,  looking  for  evidence  of  a  movement 
in  each  direction  through  the  membrane.  Why  should 
the  movement  of  the  water  into  the  tube  be  greater 
than  the  movement  in  the  opposite  direction  ?  (If  the 
thistle  tube  has  a  very  slender  stem,  it  is  better  to  fill 
the  bulb  before  tying  on  the  membrane.  The  opening 
in  the  stem  may  be  plugged  during  the  process  of 
filling.) 

NOTE.  —  With  a  special  piece  of  apparatus,  known  as 
an  osmosometer,  the  principle  of  osmosis  may  be  more 
easily  illustrated  than  by  the  method  in  either  of  the  above  experiments 
(Fig.  32).     This  apparatus  may  be  obtained  from  supply  houses. 


FIG.  32.  —  An 
osmosometer. 


CHAPTER  VII 
RESPIRATION 

THROUGH  the  movements  of  the  blood  and  the  lymph, 
materials  entering  the  body  are  transported  to  the  cells, 
and  wastes  formed  at  the  cells  are  carried  to  the  organs 
which  remove  them  from  the  body.  We  are  now  to  con- 
sider the  passage  of  materials  from  outside  the  body  to  the 
cells  and  vice  versa.  One  substance  which  the  body 
constantly  needs  is  oxygen,  and  one  which  it  is  constantly 
throwing  off  is  carbon  dioxide.  Both  of  these  are  constit- 
uents of 

The  Atmosphere.  —  The  atmosphere,  or  air,  completely 
surrounds  the  earth  as  a  kind  of  envelope,  and  comes  in 
contact  with  everything  upon  its  surface.  It  is  composed 
chiefly  of  oxygen  and  nitrogen,1  but  it  also  contains  a 
small  per  cent  of  other  substances,  such  as  water-vapor, 
carbon  dioxide,  and  argon.  All  of  the  regular  constituents 
of  the  atmosphere  are  gases,  and  these,  as  compared  with 
liquids  and  solids,  are  very  light.  Nevertheless  the  atmos- 
phere has  weight  and,  on  this  account,  exerts  pressure 
upon  everything  on  the  earth.  At  the  sea  level,  its 
pressure  is  nearly  fifteen  pounds  to  the  square  inch.  The 
atmosphere  forms  an  essential  part  of  one's  physical 
environment  and  serves  various  purposes.  The  process 

1  Oxygen  forms  about  21  per  cent  of  the  atmosphere,  nitrogen  about  78  per 
cent,  carbon  dioxide  about  .03  per  cent,  and  the  recently  discovered  element  argon 
about  i  per  cent.  The  oxygen  is  in  a  free,  or  uncombined,  condition  — the  form 
in  which  it  can  be  used  in  the  body. 

76 


RESPIRATION  77 

by  which  gaseous  materials  are  made  to  pass  between  the 
body  and  the  atmosphere  is  kjiown  as 

Respiration.  —  As  usually  denned,  respiration,  or  breath- 
ing, consists  of  two  simple  processes  —  that  of  taking  air 
into  special  contrivances  in  the  body,  called  the  lungs,  and 
that  of  expelling  air  from  the  lungs.  The  first  process 
is  known  as  inspiration;  the  second  as  expiration.  We 
must,  however,  distinguish  between  respiration  by  the 
lungs,  called  external  respiration,  and  respiration  by  the 
cells,  called  internal  respiration. 

The  purpose  of  respiration  is  indicated  by  the  changes 
that  take  'place  in  the  air  while  it  is  in  the  lungs.  Air 
entering  the  lungs  in  ordinary  breathing  parts  with  about 
five  per  cent  of  itself  in  the  form  of  oxygen  and  receives 
about  four  and  one  half  per  cent  of  carbon  dioxide,  con- 
siderable water-vapor,  and  a  small  amount  of  other  im- 
purities. These  changes  suggest  a  twofold  purpose  for 
respiration  : 

1.  To  obtain  from  the  atmosphere  the  supply  of  oxygen 
needed  by  the  body. 

2.  To    transfer    to    the    atmosphere    certain    materials 
(wastes)  which  must  be  removed  from  the  body. 

The  chief  organs  concerned  in  the  work  of  respiration 
are 

The  Lungs.  —  The  lungs  consist  of  two  sac-like  bodies 
suspended  in  the  thoracic  cavity,  and  occupying  all  the 
space  not  taken  up  by  the  heart.  They  are  not  simple 
sacs,  however,  but  are  separated  into  numerous  divisions, 
as  follows : 

1.  The  lung  on  the  right  side  of  the  thorax,  called  the 
right  lung,  is  made  up  of  three  divisions,  or  lobes,  and 
the  left  lung  is  made  up  of  two  lobes. 

2.  The  lobes  on  either  side  are  separated  into  smaller 


THE   VITAL   PROCESSES 


Larynx 


divisions,  called  lobules  (Fig.  33)-  Each  lobule  receives  a 
distinct  division  of  an  air  tube  and  has  in  itself  the  struc- 
ture of  a  miniature  lung. 

3.    In  the  lobule  the  air  tube  divides  into  a  number  of 
smaller  tubes,  each  ending  in  a  thin-walled  sac,  called  an 

infundibulum.  The 
interior  of  the  in- 
fundibulum is  sepa- 
rated into  many  small 
spaces,  known  as  the 
alveoli,  or  air  cells. 

The  lungs  are  re- 
markable for  their 
lightness  and  deli- 
cacy of  structure.1 
They  consist  chiefly 
of  the  tissues  that 
form  their  sacs,  air 
tubes,  and  blood  ves- 
sels ;  the  membranes 
that  line  their  inner 
and  outer  surfaces ; 

and    the    connective 
FIG.    33.  —  Lungs  and  air  passages  seen     . 

from  the  front.  The  right  lung  shows  the  lobes  tlSSUC  that  binds 
and  their  divisions,  the  lobules.  The  tissue  of  these  parts  together, 
the  left  lung  has  been  dissected  away  to  show  J±\\  these  tissues  are 
the  air  tubes.  i  i 

more    or    less    elas- 
tic.    The  relation  of  the  different  parts  of  the  lungs  to 

1  The  peculiar  work  devolving  upon  the  organs  of  respiration  necessitates  a 
special  plan  of  construction  —  one  adapted  to  the  properties  of  the  atmosphere. 
Being  concerned  in  the  movement  of  air,  a  gaseous  substance,  they  will  naturally 
have  a  structure  different  from  the  organs  of  circulation  which  move  a  liquid 
(the  blood).  All  the  organs  of  the  body  are  adapted  by  their  structure  to  the  work 
which  they  perform. 


RESPIRATION 


79 


each  other  and  to  the  outside  atmosphere  will  be   seen 
through  a  study  of  the 

Air  Passages.  —  The  air  passages  consist  of  a  system  of 
tubes  which  form  a  continuous  passageway  between  the 
outside  atmosphere  and  the  different  divisions  of  the  lungs. 
The  air  passes  through  them  as  it  enters  and  leaves  the 
lungs,  a  fact  which  accounts  for  the  name. 

The  incoming  air  first  enters  the  nostrils.  These  consist 
of  two  narrow  passages  lying  side  by  side  in  the  nose,  and 
connec'ting  with  the  pharynx 
behind.  The  lining  of  the 
nostrils,  called  mucous  mem- 
brane, is  quite  thick,  and  has 
its  surface  much  extended 
by  reason  of  being  spread 
over  some  thin,  scroll-shaped 
bones  that  project  into  the 
passage.  This  membrane 
is  well  supplied  with  blood 
vessels  and  secretes  a  con- 
siderable quantity  of  liquid. 
Because  of  the  nature  and 
arrangement  of  the  mem- 
brane, the  nostrils  are  able  pIG>  34. —  Model  of  section 
to  warm  and  moisten  the  through  the  head,  showing  upper  air 
incoming  air,  and  to  free  it  passages  and  other  parts,  i.  Left  nos- 
..  ,  .  .  ,.,  .  tril.  2.  Pharynx.  3.  Tongue  and  cav- 

from  dust  particles,  preparing    ityofmouth>  4.  Larynx.  5.  Trachea. 
it,  in  -this  way,  for  entrance    (,.  Esophagus, 
into  the  lungs  (Fig.  34). 

The  nostrils  are  separated  from  the  mouth  by  a  thin 
layer  of  bone,  and  back  of  both  the  mouth  and  the  nostrils 
is  the  pharynx.  The  pharynx  and  the  month  serve  as 
parts  of  the  food  canal,  as  well  as  air  passages,  and  are 


8o  THE   VITAL   PROCESSES 

described  in  connection  with  the  organs  of  digestion 
(Chapter  X).  Air  entering  the  pharynx,  either  by  the 
nostrils  or  by  the  mouth,  passes  through  it  into  the  larynx. 
The  larynx,  being  the  special  organ  for  the  production  of 
the  voice,  is  described  later  (Chapter  XXI).  The  entrance 
into  the  larynx  is  guarded  by  a  movable  lid  of  cartilage, 
called  the  epiglottis,  which  prevents  food  particles  and 
liquids,  on  being  swallowed,  from  passing  into  the  lower  air 
tubes.  The  relations  of  the  nostrils,  mouth,  pharynx,  and 
larynx  are  shown  in  Fig.  34. 

From  the  larynx  the  air  enters  the  trachea,  or  windpipe. 
This  is  a  straight  and  nearly  round  tube,  slightly  less  than 
an  inch  in  diameter  and  about  four  and  one  half  inches  in 
length.  Its  walls  contain  from  sixteen  to  twenty  C-shaped, 
cartilaginous  rings,  one  above  the  other  and  encircling  the 
tube.  These  incomplete  rings,  with  their  openings  directed 
backward,  are  held  in  place  by  thin  layers  of  connective 
and  muscular  tissue.  At  the  lower  end  the  trachea  divides 
into  two  branches,  called  the  bronchi,  each  of  which  closely 
resembles  it  in  structure.  Each  bronchus  separates  into  a 
number  of  smaller  divisions,  called  the  bronchial  tubes,  and 
these  in  turn  divide  into  still  smaller  branches,  known  as 
the  lesser  bronchial  tubes  (Fig.  33).  The  lesser  bronchial 
tubes,  and  the  branches  into  which  they  separate,  are  the 
smallest  of  the  air  tubes.  One  of  these  joins,  or  expands 
into,  each  of  the  minute  lung  sacs,  orinfundibula.  Mucous 
membrane  lines  all  of  the  air  passages. 

General  Condition  of  the  Air  Passages.  —  One  necessary 
condition  for  the  movement  of  the  air  into  and  from  the 
lungs  is  an  unobstructed  passageway.1  The  air  passages 

1  In  ordinary  inspirations  the  force  that  causes  the  air  to  move  through  the 
passages  is  scarcely  an  ounce  to  the  square  inch,  while  in  forced  inspirations  it 
does  not  exceed  half  a  pound.  On  this  account  the  closing  of  any  of  the  air  pas- 


RESPIRATION 


8l 


must  be  kept  open  and  free  from  obstructions.  They  are 
kept  open  by  special  contrivances  found  in  their  walls 
which,  by  supplying  a  degree  of  stiffness,  cause  the  tubes 
to  keep  their  form.  In  the  trachea,  bronchi,  and  larger 
bronchial  tubes,  the  stiffness  is  supplied  by  rings  of  carti- 
lage, while  in  the  smaller  tubes  this  is  replaced  by  connect- 
ive and  muscular  tissue.  The  walls  of  the  larynx  contain 
strips  and  plates  of  cartilage ;  while  the  nostrils  and  the 
pharynx  are  kept  open  by  their  bony  surroundings. 

The  air  passages  are  kept  clean  by  cells  especially 
adapted  to  this  purpose,  known  as  the  ciliated  epithelial 
cells.  These  are  slender,  wedge-shaped  cells  which  have 
projecting  from  a  free  end  many  small,  hair-like  bodies, 
called  cilia  (Fig.  35).  They  line  the  mucous  membrane 

in    most   of    the   air 

j 
passages,  and  are  so 

placed  that  the  cilia 
project  into  the  tubes. 
Here  they  keep  up 
an  inward  and  out- 
ward wave-like  move- 
ment, which  is 
quicker  and  has 
greater  force  in  the 
outward  direction.  By  this  means  the  cilia  are  able  to 
move  small  pieces  of  foreign  matter,  such  as  dust  particles 
and  bits  of  partly  dried  mucus,  called  phlegm,  to  places 
where  they  can  be  easily  expelled  from  the  lungs.1 

sages  by  pressure,  or  by  the  presence  of  foreign  substances,  would  keep  the  air  from 
reaching  some  part  of  the  lungs. 

1  Coughing,  which  is  a  forceful  expulsion  of  air,  has  for  its  purpose  the  ejection 
of  foreign  substances  from  the  throat  and  lungs.  Sneezing,  on  the  other  hand,  has 
for  its  purpose  the  cleansing  of  the  nostrils.  In  coughing,  the  air  is  expelled 
through  the  mouth,  while  in  sneezing  it  is  expelled  through  the  nostrils. 


B 

FIG.  35.  —  Ciliated  epithelial 
A   cells.    A.  Two  cells  highly  mag- 
nified,   c.  Cilia.    «.  Nucleus.    B. 
Diagram    of   a    small    air     tube 
showing  the  lining  of  cilia. 


82 


THE   VITAL   PROCESSES 


The  Alveoli.  —  The  alveoli,  or  air  cells,  are  the  small  divi- 
sions of  the  inf  undibula  (Fig.  36).  They  are  each  about  one 
one-hundredth  of  an  inch  (|  mm.)  in 
diameter,  being  formed  by  the  infolding 
of  the  infundibular  wall.  This  wall, 
which  has  for  its  framework  a  thin 
layer  of  elastic  connective  tissue,  sup- 
ports a  dense  network  of  capillaries 
(Fig.  37),  and  is  lined  by  a  single  layer 
of  cells  placed  edge  to  edge.  By  this 

arrangement  the   air  within  the  alveoli 
FIG.  36.  — Termi- 
nal air  sacs.     The    1S   brought  very  near   a  large  surface 

two  large  sacs  are  in-  of  blood,  and  the  exchange  of  gases 
between  the  air  and  the  blood  is  made 
possible.  It  is  at  the  alveoli  that  the 
oxygen  passes  from  the  air  into  the 

blood,  and  the  carbon  dioxide  passes  from  the  blood  into 

the  air.     At  no  place  in 

the  lungs,  however,  do 

the   air   and   the   blood 

come  in  direct  contact. 

Their    exchanges    must 

in  all  cases  take  place 

through     the     capillary 

walls  and  the  layer  of 

cells  lining  the  alveoli. 
Blood   Supply  to   the 

Lungs. — To  accomplish 

the  purposes  of  respira- 
tion,   not  only  the   air, 


fundibula;  the  small 
divisions  are  alveoli. 
(Enlarged.) 


FIG.  37. —  Inner  lung  surface  (magni- 


fied), the  blood  vessels  injected  with  color- 
but  the  blood  also,  must  ~,  .      .. 

mg  matter.      I  he  small  pits  are  alveoli, 

be  passed  into  and  from      and  the  vessels  in  their  walls  are  chiefly 
the    lungs.        The    chief      capillaries. 


RESPIRATION 


FIG.  38. 


AIR 


FIG.  39. 

FIG.  38.  —  Diagram  to  show  the  double  movement  of  air  and  blood 
through  the  lungs.  The  blood  leaves  the  heart  by  the  pulmonary  artery 
and  returns  by  the  pulmonary  veins.  The  air  enters  and  leaves  the  lungs  by 
the  same  system  of  tubes. 

FIG.  39.  —  Diagram  to  show  air  and  blood  movements  in  a  terminal 
air  sac.  While  the  air  moves  into  and  from  the  space  within  the  sac,  the 
blood  circulates  through  the  sac  walls. 


g4  THE   VITAL   PROCESSES 

artery  conveying  blood  to  the  lungs  is  fas  pulmonary  artery. 
This  starts  at  the  right  ventricle  and  by  its  branches  con- 
veys blood  to  the  capillaries  surrounding  the  alveoli  in  all 
parts  of  the  lungs.  The  branches  of  the  pulmonary  artery 
lie  alongside  of,  and  divide  similarly  to,  the  bronchial 
tubes.  At  the  places  where  the  finest  divisions  of  the  air 
tubes  enter  the  infundibula,  the  little  arteries  branch  into 

the  capillaries  that  pene- 
trate the  infundibular  walls 
(Figs.  38  and  39).  From 
these  capillaries  the  blood 
is  conveyed  by  the  pulmo- 
nary veins  to  the  left 
auricle. 

The   lungs  also  receive  blood 

FIG.  40. -The  pleura.  Diagram  from  two  (in  some  individuals 
showing  the  general  form  of  the  pleural  three)  sma11  arteries  branching 
sacs  as  they  surround  the  lungs  and  fr°m  the  aorta,  known  as  the 
line  the  inner  surfaces  of  the  chest  bronchial  arteries.  These  con- 
Other  parts  removed).  A,  A'.  Places  vey  to  the  lungs  blood  that  has 
occupied  by  the  lungs.  B,  B' .  Slight  already  been  supplied  with  oxy- 
space  within  the  pleural  sacs  contain-  gen,  passing  it  into  the  capilla- 
ing  the  pleural  secretion,  a,  a\  Outer  ries  in  the  walls  of  the  bronchi, 
layer  of  pleura  and  lining  of  chest  bronchial  tubes,  and  large  blood 
walls  and  upper  surface  of  diaphragm,  vessels,  as  well  as  the  connect- 
6,  b'.  Inner  layer  of  pleura  and  outer  ive  tissue  between  the  lobes  of 
lining  of  lungs.  C.  Space  occupied  the  lungs>  Thig  blood  leayes 
by  the  heart.  D.  Diaphragm.  thg  ]ungs  parUy  by  the  bron. 

chial  veins  and  partly  by  the  pulmonary  veins.     No  part  of  the  body 
is  so  well  supplied  with  blood  as  the  lungs. 

The  Pleura.  —  The  pleura  is  a  thin,  smooth,  elastic,  and 
tough  membrane  which  covers  the  outside  of  the  lungs 
and  lines  the  inside  of  the  chest  walls.  The  covering  of 
each  lung  is  continuous  with  the  lining  of  the  chest  wall 
on  its  respective  side  and  forms  with  it  a  closed  sac  by 


RESPIRATION  85 

which  the  lung  is  surrounded,  the  arrangement  being  simi- 
lar to  that  of  the  pericardium.  Properly  speaking,  there 
are  two  pleurae,  one  for  each  lung,  and  these,  besides 
inclosing  the  lungs,  partition  off  a  middle  space  which  is 
occupied  by  the  heart  (Fig.  40).  They  also  cover  the 
upper  surface  of  the  diaphragm,  from  which  they  deflect 
upward,  blending  with  the  pericardium.  A  small  amount 
of  liquid  is  secreted  by  the  pleura,  which  prevents  friction 
as  the  surfaces  glide  over  each  other  in  breathing. 

The  Thorax.  —  The  force  required  for  breathing  is  sup- 
plied by  the  box-like  portion  of  the  body  in  which  the 
lungs  are  placed.  This  is  known  as  the  thorax,  or  chest, 
and  includes  that  part  of  the  trunk  between  the  neck  arid 
the  abdomen.  The  space  which  it  incloses,  known  as  the 
thoracic  cavity,  is  a  variable  space  and  the  walls  surround- 
ing this  space  are  air-tight.  A  framework  for  the  thorax 
is  supplied  by  the  ribs  which  connect  with  the  spinal 
column  behind  and  with  the  sternum,  or  breast-bone,  in 
front.  They  form  joints  with  the  spinal  column,  but  con- 
nect with  the  sternum  by  strips  of  cartilage.  The  ribs  do 
not  encircle  the  cavity  in  a  horizontal  direction,  but  slope 
downward  from  the  spinal  column  both  toward  the  front 
and  toward  the  sides,  this  being  necessary  to  the  service 
which  they  render  in  breathing. 

How  Air  is  Brought  into  and  Expelled  from  the  Lungs.  — 
The  principle  involved  in  breathing  is  that  air  flows  from 
a  place  of  greater  to  a  place  of  less  pressure.  The  con- 
struction of  the  thorax  and  the  arrangement  of  the  lungs 
within  it  provide  for  the  application  of  this  principle  in  a 
most  practical  manner.  The  lungs  are  suspended  from 
the  upper  portion  of  the  thoracic  cavity,  and  the  trachea 
and  the  upper  air  passages  provide  the  only  opening  to 
the  outside  atmosphere.  Air  entering  the  thorax  must  on 


86 


THE   VITAL   PROCESSES 


this  account  pass  into  the  lungs.  As  the  thorax  is 
enlarged  the  air  in  the  lungs  expands,  and  there  is  pro- 
duced within  them  a  place  of  slightly  less  air  pressure 
than  that  of  the  atmosphere  on  the  outside  of  the  body. 
This  difference  causes  the  air  to  flow  into  the  lungs. 

When  the  thorax  is  diminished  in  size,  the  air  within  the 
lungs  is  slightly  compressed.     This  causes  it  to  become 
denser  and  to  exert  on  this  account   a   pressure  slightly 
greater  than  that  of  the  atmosphere  on  the  outside.     The 
air  now  flows   out  until  the  equality  of  the 
pressure  is  again  restored.     Thus  the  thorax, 
by  making  the  pressure  within  the  lungs  first 
slightly  less  and   then  slightly  greater  than 
the  atmospheric  pressure,  causes 
the  air  to   move    into   and  out 
of  the  lungs. 

Breathing  is  well  illustrated  by 
means  of  the  common  hand  bellows, 
its  action  being  similar  to  that  of  the 
thorax.  It  will  be  observed  that  when 
the  sides  are  spread  apart  air  flows  into 
B  the  bellows.  When  they  are  pressed 
FIG.  41. -Diagram  illustrat-  together  the  air  flows  out.  If  an  air- 
ing  the  bellows  principle  in  tiSht  sack  were  hung  ln  the  bellows 
breathing.  A.  The  human  bel-  with  its  mouth  attached  to  the  project- 
lows.  B.  The  hand  bellows,  ing  tube,  the  arrangement  would 
Compare  part  for  part.  resemble  closely  the  general  plan  of 

the  breathing  organs  (Fig.  41).     One 

respect,  however,  in  which  the  bellows  differs  from  the  thorax  should 
be  noted.  The  thorax  is  never  sufficiently  compressed  to  drive  out 
all  the  air.  Air  is  always  present  in  the  lungs.  This  keeps  them 
more  or  less  distended  and  pressed  against  the  thoracic  walls. 

How  the  Thoracic  Space  is  Varied.  —  One  means  of  vary- 
ing the  size  of  the  thoracic  cavity  is  through  the  move- 
ments of  the  ribs  and  their  resultant  effect  upon  the  walls 


RESPIRATION  8/ 

of  the  thorax.  In  bringing  about  these  movements  the 
following  muscles  are  employed: 

1.  The  scaleni  muscles,  three  in  number  on  each  side,  which  con- 
nect at  one  end  with  the  vertebras  of  the  neck  and  at  the  other  with  the 
first  and  second   ribs.     Their   contraction   slightly   raises   the   upper 
portion  of  the  thorax. 

2.  The  elevators  of  the  ribs,  twelve  in  number  on  each  side,  which 
are  so  distributed  that  each  single  muscle  is  attached,  at  one  end,  to  the 
back  portion  of  a  rib  and,  at  the  other,  to  a  projection  of  the  vertebra 
a  few  inches  above.     The  effect  of  their  contraction  is  to  elevate  the 
middle  portion  of  the  ribs  and  to  turn  them  outward  or  spread  them 
apart. 

.  3.  The  intercostal  muscles,  which  form  two  thin  layers  between  the 
ribs,  known  as  the  internal  and  the  external  intercostal  muscles.  The 
external  intercostals  are  attached  between  the  outer  lower  margin  of 
the  rib  above  and  the  outer  upper  margin  of  the  rib  below,  and 
extend  obliquely  downward  and  forward.  The  internal  intercostals  are 
attached  between  the  inner  margins  of  adjacent  ribs,  and  they  extend 
obliquely  downward  and  backward  from  the  front.  The  contraction  of 
the  external  intercostal  muscles  raises  the  ribs,  and  the  contraction 
of  the  internal  intercostals  tends  to  lower  them. 

By  slightly  raising    and  spreading  apart  the   ribs  the 
thoracic  space  is  increased  in  two  directions  —  from  front 

FIG.  42.  —  Simple  apparatus  for  illustrating  effect  of  move- 
ments of  the  ribs  upon  the  thoracic  space  ;  strips  of  card- 
board held  together  by  pins,  the  front  part  being  raised  or 
lowered  by  threads  moving  through  attachments  at  I  and  2. 
As  the  front  is  raised  the  space  between  the  uprights  is  in- 
creased. The  front  upright  corresponds  to  the  breastbone,  the 
back  one  to  the  spinal  column,  the  connecting  strips  to  the 
ribs,  and  the  threads  to  the  intercostal  muscles. 

to  back  and  from  side  to  side.  Lowering  and  converg- 
ing the  ribs  has,  of  course,  the  opposite  effect  (Fig.  42). 
Except  in  forced  expirations  the  ribs  are  lowered  and  con- 
verged by  their  own  weight  and  by  the  elastic  reaction  of 
the  surrounding  parts, 


88  THE   VITAL   PROCESSES 

The  Diaphragm.  —  Another  means  of  varying  the 
thoracic  space  is  found  in  an  organ  known  as  the  dia- 
phragm. This  is  the  dome-shaped,  movable  partition 
which  separates  the  thoracic  cavity  from  the  cavity  of  the 
abdomen.  The  edges  of  the  diaphragm  are  firmly  attached 
to  the  walls  of  the  trunk,  and  the  center  is  supported  by 
the  pericardium  and  the  pleura.  The  outer  margin  is 
muscular,  but  the  central  portion  consists  of  a  strong  sheet 
of  connective  tissue.  By  the  contraction  of  its  muscles 
the  diaphragm  is  pulled  down,  thereby  increasing  the 
thoracic  cavity.  By  raising  the  diaphragm  the  thoracic 
cavity  is  diminished. 

The  diaphragm,  however,  is  not  raised  by  the  contraction 
of  its  own  muscles,  but  \%  pushed  up  by  the  organs  beneath. 
By  the  elastic  reaction  of  the  abdominal  walls  (after  their 
having  been  pushed  out  by  the  lowering  of  the  diaphragm), 
pressure  is  exerted  on  the  organs  of  the  abdomen  and 
these  in  turn  press  against  the  diaphragm.  This  crowds 
it  into  the  thoracic  space.  In  forced  expirations  the 
muscles  in  the  abdominal  walls  contract  to  push  up  the 
diaphragm. 

Interchange  of  Gases  in  the  Lungs.  —  During  each  inspiration  the 
air  from  the  outside  fills  the  entire  system  of  bronchial  tubes,  but  the 
alveoli  are  largely  filled,  at  the  same  time,  by  the  air  which  the  last  ex- 
piratory effort  has  left  in  the  passages.  By  the  action  of  currents  and 
eddies  and  by  the  rapid  diffusion  of  gas  particles,  the  air  from  the  out- 
side mixes  with  that  in  the  alveoli  and  comes  in  contact  with  the  mem- 
branous walls.  Here  the  oxygen,  after  being  dissolved  by  the  moisture 
in  the  membrane,  diffuses  into  the  blood.  The  carbon  dioxide,  on  the 
other  hand,  being  in  excess  in  the  blood,  diffuses  toward  the  air  in  the 
alveoli.  The  interchange  of  gases  at  the  lungs,  however,  is  not  fully 
understood,  and  it  is  possible  that  other  forces  than  osmosis  play  a 
part. 

Capacity  of  the  Lungs.  —  The  air  which  passes  into  and  from  the 
lungs  in  ordinary  breathing,  called  the  tidal  air,  is  but  a  small  part  of 


RESPIRATION 


89 


the  whole  amount  of  air  which  the  lungs  contain.     Even  after  a  forced 

expiration  the  lungs  are  almost  half  full ;    the  air  which  remains   is 

called  the  residual  air.      The  air 

which  is  expelled  from  the  lungs 

by  a  forced   expiration,    less   the 

tidal  air,  is  called  the  reserve,  or 

supplemental,  air.     These   several 

quantities     are     easily    estimated. 

(See    Practical    Work.)      In    the 

average  individual  the  total  capacity 

of  the   lungs    (with   the   chest   in 

repose)  is  about  one  gallon.      In 

forced  inspirations  this  capacity  may 

be  increased  about  one  third,  the 

excess  being  known   as  the  com- 

plemental air  (Fig.  43). 

FIG.  43.  —  Diagram  illustrating  lung 

Internal,  or  Cell,  Respira-  capacity, 

tion.  --  The    oxygen    which 

enters  the  blood  in  the  lungs  leaves  it  in  the  tissues,  passing 
through  the  lymph  into  the  cells  (Fig.  44).     At  the  same 


Lymph 


FIG.  44.  —  Diagram  illustrating  internal  respiration  and  its  dependence  on 
external  respiration.     (Modified  from  Hall.)     (See  text.) 

time  the  carbon  dioxide  which  is  being  formed  at  the  cells 
passes  into  the  blood.  An  exchange  of  gases  is  thus 
taking  place  between  the  cells  and  the  blood,  similar  to 


9o 


THE   VITAL  PROCESSES 


that  taking  place  between  the  blood  and  the  air.  This 
exchange  is  known  as  internal,  or  cell,  respiration.  By 
internal  respiration  the  oxygen  reaches  the  place  where  it 
is  to  serve  its  purpose,  and  the  carbon  dioxide  begins  its 
movement  toward  the  exterior  of  the  body.  This 
"  breathing  by  the  cells "  is,  therefore,  the  final  and 
essential  act  of  respiration.  Breathing  by  the  lungs  is 
simply  the  means  by  which  the  taking  up  of  oxygen  and 
the  giving  off  of  carbon  dioxide  by  the  cells  is  made 
possible. 

HYGIENE  OF   RESPIRATORY  ORGANS 

The  liability  of  the  lungs  to  attacks  from  such'  dread 
diseases  as  consumption  and  pneumonia  makes  questions 
touching  their  hygiene  of  first  importance.  Consumption 
does  not  as  a  rule  attack  sound  lung  tissue,  but  usually 
has  its  beginning  in  some  weak  or  enfeebled  spot  in  the 
lungs  which  has  lost  its  "power  of  resistance."  Though 
consumption  is  not  inherited,  as  some  suppose,  lung  weak- 
nesses may  be  transmitted  from  parents  to  children.  This, 
together  with  the  fact,  now  generally  recognized,  that  con- 
sumption is  contagious,  accounts  for  the  frequent  appear- 
ance of  this  disease  in  the  same  family.  Consumption 
as  well  as  other  respiratory  affections  can  in  the  majority 
of  cases  be  prevented,  and  in  many  cases  cured,  by  an  in- 
telligent observation  of  well-known  laws  of  health. 

Breathe  through  the  Nostrils.  —  Pure  air  and  plenty  of  it  is 
the  main  condition  in  the  hygiene  of  the  lungs.  One  nec- 
essary provision  for  obtain  ing  pure  air\s>  that  of  breathing 
through  the  nostrils.  Air  is  the  carrier  of  dust  particles 
and  not  infrequently  of  disease  germs.1  Partly  through 

1  The  amount  of  dust  suspended  in  what  we  ordinarily  think  of  as  pure  air  is 
shown  when  a  beam  of  direct  sunlight  enters  an  otherwise  darkened  room. 


RESPIRATION 


the  small  hairs  in  the  nose,  but  mainly  through  the  moist 

membrane  that  lines  the   passages,  the  nostrils  serve  as 

niters  for  removing  the  minute  solid  particles  (Fig.  45). 

While   it  is  important  that 

nose  breathing  be  observed 

at  all  times,  it  is  especially 

important  when  one  is  sur- 

rounded by  a  dusty  or  smoky 

atmosphere.     Otherwise  the 

small     particles     that     are 

breathed     in     through     the 

mouth    may  find  a    lodging 

place  in  the  lungs. 

In  addition  to  removing 
dust  particles  and  germs, 
other  purposes  are  served 


FK,  45.  -  Human  air  filter.     Di- 

agram  of  a  section  through  the  nos- 

trils  .  shows  projecting  bones  covered 

nostrils.        The    warmth    and    with    moist  membrane  against   which 
moisture    which    the    air    re-     the  air  is  made  to  strike  by  the  narrow 

uu     '•  Air  Passaees-   ^.  Cavities 

in  the  bones.      3.    Front  lower  portion 


,         . 

by   breathing   through    the 


ceives  in  this  way,  prepare     assages- 


, 

it    for    entering   the    lungs.    of  the  cranial  cavity. 

Mouth    breathing,    on    the 

other  hand,  looks  bad    and   during  sleep  causes  snoring. 

The  habit  of  nose  breathing  should  be  established  early 

in  life.1 

Cultivate  Full  Breathing.  —  Many  people,  while  appar- 
ently taking  in  sufficient  air  to  supply  their  need  for 
oxygen,  do  not  breathe  deeply  enough  to  "  freely  venti- 
late the  lungs."  "  Shallow  breathing,"  as  this  is  called, 

1  Some  children  find  it  difficult  to  breathe  through  the  nostrils  on  account  of 
growths  (called  adenoids)  in  the  upper  pharynx.  Such  children  should  have 
medical  attention.  The  removal  of  these  growths  not  only  improves  the  method  of 
breathing,  but  in  many  instances  causes  a  marked  improvement  in  the  general 
health  and  personal  appearance. 


g2  THE   VITAL   PROCESSES 

is  objectionable  because  it  fails  to  keep  up  a  healthy  con- 
dition of  the  entire  lung  surface.  Portions  of  the  lungs  to 
which  air  does  not  easily  penetrate  fail  to  get  the  fresh  air 
and  exercise  which  they  need.  As  a  consequence,  they 
become  weak  and,  by  losing  their  "  power  of  resistance," 
become  points  of  attack  in  diseases  of  the  lungs.1  The 
breathing  of  each  individual  should  receive  attention,  and 
where  from  some  cause  it  is  not  sufficiently  full  and  deep, 
the  means  should  be  found  for  remedying  the  defect. 

Causes  of  Shallow  Breathing.  —  Anything  that  impedes 
the  free  movement  of  air  into  the  lungs  tends  to  cause 
shallow  breathing  A  drooping  of  the  back  or  shoulders 
and  a  curved  condition  of  the  spinal  column,  such  as  is 
caused  by  an  improper  position  in  sitting,  interfere  with 
the  free  movements  of  the  ribs  and  are  recognized  causes. 
Clothing  also  may  impede  the  respiratory  movements  and 
lead  to  shallow  breathing.  If  too  tight  around  the  chest, 
clothing  interferes  with  the  elevation  of  the  ribs ;  and  if  too 
tight  around  the  waist,  it  prevents  the  depression  of  the 
diaphragm.  Other  causes  of  shallow  breathing  are  found 
in  the  absence  of  vigorous  exercise,  in  the  leading  of  an 
indoor  and  inactive  life,  in  obstructions  in  the  nostrils  and 
upper  pharynx,  and  in  the  lack  of  attention  to  proper 
methods  of  breathing. 

To  prevent  shallow  breathing  one  should  have  the  habit 
of  sitting  and  standing  erect.  The  clothing  must  not  be 
allowed  to  interfere  with  the  respiratory  movements.  The 
taking  of  exercise  sufficiently  vigorous  to  cause  deep  and 

1  The  weakest  portions  of  the  lungs  appear  to  be  the  tiny  lobes  at  the  top. 
As  they  occupy  the  part  of  the  thorax  most  difficult  to  expand,  air  penetrates  them 
much  less  freely  than  it  does  the  lobes  below.  In  most  cases  of  consumption 
(some  authorities  give  as  high  as  eighty  per  cent) ,  the  upper  lobes  are  the  first  to 
be  affected.  Flat  chests  and  round  shoulders,  by  increasing  this  natural  difficulty 
in  breathing,  have  lonr  been  recognized  as  causes  which  predispose  to  consumption. 


RESPIRATION  93 

rapid  breathing  should  be  a  common  practice  and  one 
should  spend  considerable  time  out  of  doors.  If  one  has  a 
flat  chest  or  round  shoulders,  he  should  strive  by  suitable 
exercises  to  overcome  these  defects.  Obstructions  in  the 
nostrils  or  pharynx  should  be  removed. 

Breathing  Exercises.  —  In  overcoming  the  habit  of  shal- 
low breathing  and  in  strengthening  the  lungs  generally, 
the  practicing  of  occasional  deep  breathing  has  been  found 
most  valuable  and  is  widely  recommended.  With  the 
hands  on  the  hips,  the  shoulders  .drawn  back  and  down, 
the  chest  pushed  upward  and  forward,  and  the  chin 
slightly  depressed,  draw  the  air  slowly  through  the  nostrils 
until  the  lungs  are  completely  full.  After  holding  this  long 
enough  to  count  three  slowly,  expel  it  quickly  from  the 
lungs.  Avoid  straining.  To  get  the  benefit  of  pure  air,  it 
is  generally  better  to  practice  deep  breathing  out  of  doors 
or  before  an  open  window. 

By  combining  deep  breathing  with  simple  exercises  of 
the  arms,  shoulders,  and  trunk  much  may  be  done  towards 
straightening  the  spine,  squaring  the  shoulders,  and  over- 
coming flatness  of  the  chest.  Though  such  movements  are 
best  carried  on  by  the  aid  of  a  physical  director,  one  can 
do  much  to  help  himself.  One  may  safely  proceed  on 
the  principle  that  slight  deformities  of  the  chest,  spine, 
and  shoulders  are  corrected  by  gaining  and  keeping  the 
natural  positions,  and  may  employ  any  movements  which 
will  loosen  up  the  parts  and  bring  them  where  they  natu- 
rally belong.1 

1  The  following  exercise,  from  Dudley  A.  Sargent's  Health,  Strength,  and 
Power,  will  be  found  most  beneficial :  "  Stand  with  the  feet  together,  face  down- 
ward, arms  extended  downward,  and  backs  of  the  hands  touching.  Raise  the 
hands,  arms,  and  elbows,  keeping  the  backs  of  the  hands  together  until  they  pass 
the  chest  and  face.  Then  continue  the  movement  upward,  until  the  hands  sepa- 
rate above  the  head  with  the  face  turned  upward,  when  they  should  be  brought 


94  THE   VITAL   PROCESSES 

Serious  Nature  of  Colds.  —  That  many  cases  of  consump- 
tion have  their  beginning  in  severe  colds  (on  the  lungs) 
is  not  only  a  matter  of  popular  belief,  but  the  judgment 
also  of  physicians.  Though  the  cold  is  a  different  affec- 
tion from  that  of  consumption,  it  may  so  lower  the  vitality 
of  the  body  and  weaken  the  lung  surfaces  that  the  germs 
of  consumption  find  it  easy  to  get  a  start.  On  this  account 
a  cold  on  the  chest  which  does  not  disappear  in  a  few  days, 
but  which  persists,  causing  more  or  less  coughing  and  pain 
in  the  lungs,  must  be  given  serious  consideration.1  The 
usual  home  remedies  failing  to  give  relief,  a  physician 
should  be  consulted.  It  should  also  be  noted  that  cer- 
tain diseases  of  a  serious  nature  (pneumonia,  diphtheria, 
measles,  etc.)  have  in  their  beginning  the  appearance  of 
colds.  On  this  account  it  is  wise  not  only  to  call  a  phy- 
sician, but  to  call  him  early,  in  severe  attacks  of  the  lungs. 
Especially  if  the  attack  be  attended  by  difficult  breathing, 
fever,  and  a  rapid  pulse  is  the  case  serious  and  medical 
advice  necessary. 

Ventilation.  —  The  process  by  which  the  air  in  a  room 
is  kept  fresh  and  pure  is  known  as  ventilation.  It  is  a 

downward  and  outward  in  a  large  circle  to  the  starting  point.  Begin  to  inhale  as 
the  arms  are  raised  and  take  in  as  much  air  as  possible  by  the  time  the  hands 
are  above  the  head,  then  allow  the  breath  to  go  out  slowly  as  the  arms  descend." 

1  Colds  may  frequently  be  broken  up  at  their  beginning  by  taking  a  prolonged 
hot  bath  and  going  to  bed.  After  getting  a  start,  however,  they  run  a  course  of  a 
few  days,  a  week,  or  longer,  depending  upon  the  natural  vigor  of  the  individual  and 
the  care  which  he  gives  his  body  during  the  time.  In  throwing  off  a  cold,  the 
following  suggestions  will  be  found  helpful : 

i.  Dress  warmly  (without  overdoing  it)  and  avoid  getting  chilled.  2.  Diminish 
the  usual  amount  of  work  and  increase  the  period  for  sleep.  If  very  weak,  stay  in 
bed.  Save  the  energy  for  throwing  off  the  cold.  3.  If  able  to  be  about,  spend  con- 
siderable time  in  light  exercise  out  of  doors,  but  avoid  getting  chilled.  4.  Keep 
the  bowels  active,  taking  a  cathartic  if  necessary.  5.  To  relieve  pain  in  the  chest, 
apply  a  mustard  plaster  or  a  flannel  cloth  moistened  with  some  irritating  substance, 
such  as  turpentine  or  a  mixture  of  equal  parts  of  kerosene  and  lard.  Keep  up  a 
mild  irritation  until  the  pain  is  relieved,  but  avoid  blistering. 


RESPIRATION  95 

double  process  —  that  of  bringing  fresh  air  into  the  room 
and  that  of  getting  rid  of  air  that  has  been  rendered  impure 
by  breathing  1  or  by  lamps.  Outdoor  air  is  usually  of  a 
different  temperature  (colder  in  winter,  warmer  in  summer) 
from  that  indoors,  and  as  a  consequence  differs  from  it 
slightly  in  weight.  On  account  of  this  difference,  suitable 
openings  in  the  walls  of  buildings  induce  currents  which 
pass  between  the  rooms  and  the  outside  atmosphere  even 
when  there  is  no  wind.  In  winter  care  must  be  taken  to 
prevent  drafts  and  to  avoid  too  great  a  loss  of  heat  from 
the  room.  A  cold  draft  may  even  cause  more  harm  to 
one  in  delicate  health  than  the  breathing  of  air  which  is 
impure.  To  ventilate  a  room  successfully 
the  problem  of  preventing  drafts  must  be 
considered  along  with  that  of  admitting  the 
fresh  air. 

The  method  of  ventilation  must  also  be 
adapted  to  the  construction  of  the  building, 
the  plan  of  heating,  and  the  condition  of 
the  weather.  Specific  directions  cannot  be 
given,  but  the  following  suggestions  will  be 
found  helpful  in  ventilating  rooms  where  FIG.  46.— Win- 
the  air  is  not  warmed  before  being  admitted  :  dow  adjusted  for 

1.  Introduce  the  air  through  many  small  ventilation   with- 
openings  rather  than  a  few  large  ones.     If 

the  windows  are  used  for  this  purpose,  raise  the  lower  sash 
and  drop  the  upper  one  slightly  for  several  windows,  vary- 
ing the  width  to  suit  the  conditions  (Fig.  46).  By  this  means 
sufficient  air  may  be  introduced  without  causing  drafts. 

2.  Introduce  the  air  at  tlie  warmest  portions  of  the  room. 

1  Not  only  do  the  lungs  remove  oxygen  from  the  air  and  add  carbon  dioxide  to 
it,  but  they  separate  from  the  body  considerable  moisture  and,  according  to  some 
authorities,  a  small  amount  of  an  impurity  referred  to  as  "  animal  matter."  Odors 


96  THE   VITAL   PROCESSES 

The  air  should,  if  possible,  be  warmed  before  reaching  the 
occupants. 

3.  If  the  wind  is  blowing,  ventilate  principally  on  the 
sheltered  side  of  the  house. 

Ample  provision  should  be  made  for  fresh  air  in  sleep- 
ing rooms,  and  here  again  drafts  must  be  avoided.  Espe- 
tcially  should  the  bed  be  so  placed  that  strong  air  currents 
do  not  pass  over  the  sleeper.  In  schoolhouses  and  halls 
for  public  gatherings  the  means  for  efficient  ventilation 
should,  if  possible,  be  provided  in  the  general  plan  of 
construction  and  method  of  heating. 


FIG.  47.  —  Artificial  respiration  as  a  laboratory  experiment.     Expiration. 
Prone-posture  method  of  Schaffer. 

Artificial  Respiration.  —  When  natural  breathing  is  temporarily  sus- 
pended, as  in  partial  drowning,  or  when  one  has  been  overcome  by 
breathing  some  poisonous  gas,  the  saving  of  life  often  depends  upon 
the  prompt  application  of  artificial  respiration.  This  is  accomplished 
by  alternately  compressing  and  enlarging  the  thorax  by  means  of  vari- 
able pressure  on  the  outside,  imitating  the  natural  process  as  nearly  as 
possible.  Following  is  the  method  proposed  by  Professor  E.  A. 
Schaffer  of  England,  and  called  by  him  "  the  prone-posture  method 
of  artificial  respiration  "  : 

also  arise  from  the  skin,  teeth,  and  clothing  which,  if  not  dangerous  to  the  health, 
are  offensive  to  the  nostrils.  If  on  going  into  a  room  such  odors  are  detected,  the 
ventilation  is  not  sufficient.  This  is  said  to  be  a  reliable  test. 


RESPIRATION 


97 


The  patient  is  laid  face  downward  with  an  arm  bent  under  the  head, 
and  intermittent  pressure  applied  vertically  over  the  shortest  ribs.  The 
pressure  drives  the  air  from  the  lungs,  both  by  compressing  the  lower 
portions  of  the  chest  and  by  forcing  the  abdominal  contents  against 
the  diaphragm,  while  the  elastic  reaction  of  the  parts  causes  fresh  air 
to  enter  (Figs.  47  and  48).  "The  operator  kneels  or  squats  by  the 
side  of,  or  across  the  patient,  places  his  hands  over  the  lowest  ribs  and 
swings  his  body  backward  and  forward  so  as  to  allow  his  weight  to 


FIG.  48.  —  Artificial  respiration.     Inspiration. 

fall  vertically  on  the  wrists  and  then  to  be  removed ;  in  this  way  hardly 
any  muscular  exertion  is  required.  .  .  .  The  pressure  is  applied  grad- 
ually and  slowly,  occupying  some  three  seconds  ;  it  is  then  withdrawn 
during  two  seconds  and  again  applied ;  and  so  on  some  twelve  times 
per  minute."  * 

The  special  advantages  of  the  prone-posture  method  over  others  that 
have  been  employed  are:  i.  It  may  be  applied  by  a  single  individual 
and  for  a  long  period  of  time  without  exhaustion.  2.  It  allows  the 
mucus  and  water  (in  case  of  drowning)  to  run  out  of  the  mouth,  and 
causes  the  tongue  to  fall  forward  so  as  not  to  obstruct  the  passageway. 
3.  It  brings  a  sufficient  amount  of  air  into  the  lungs.2 

1  E.  A.  Schaffer,  "Artificial  Respiration  in  its  Physiologic  Aspects,"  The  Journal 
of  the  American  Medical  Association,  September,  1908. 

2  Testing  the  prone-posture  method  by  suitable  apparatus,  Professor  Schaffer  has 
found  it  capable  of  introducing  more  air  per  minute  into  the  lungs  than  any  of  the 
other  methods  of  artificial  respiration,  and  more  even  than  is  introduced  by  ordi- 
nary breathing. 


gS  THE   VITAL   PROCESSES 

While  applying  artificial  respiration,  the  heat  of  the  body  should  not 
be  allowed  to  escape  any  more  than  can  possibly  be  helped.  In  case 
of  drowning,  the  patient  should  be  wrapped  in  dry  blankets  or  clothing, 
while  bottles  of  hot  water  may  be  placed  in  contact  with  the  body. 
The  circulation  should  be  stimulated,  as  may  be  done  by  rubbing  the 
hands,  feet,  or  limbs  in  the  direction  of  the  flow  of  the  blood  in  the 
veins. 

Tobacco  Smoke  and  the  Air  Passages.  —  Smoke  consists 
of  minute  particles  of  unburnt  carbon,  or  soot,  such  as 
collect  in  the  chimneys  of  fireplaces  and  furnaces.  If  much 
smoke  is  taken  into  the  lungs,  it  irritates  the  delicate  linings 
and  tends  to  clog  them  up.  Tobacco  smoke  also  contains 
the  poison  nicotine,  which  is  absorbed  into  the  blood.  For 
these  reasons  the  cigarette  user  who  inhales  the  smoke  does 
himself  great  harm,  injuring  his  nervous  system  and  laying 
the  foundation  for  diseases  of  the  air  passages.  The  prac- 
tice of  smoking  indoors  is  likewise  objectionable,  since 
every  one  in  a  room  containing  the  smoke  is  compelled  to 
breathe  it. 

Alcohol  and  Diseases  of  the  Lungs.  —  Pneumonia  is  a 
serious  disease  of  the  lungs  caused  by  germs.  The  attacks 
occur  as  a  result  of  exposure,  especially  when  the  body  is 
in  a  weakened  condition.  A  noted  authority  states  that 
"alcoholism  is  perhaps  the  most  potent  predisposing 
cause"  of  pneumonia.1  A  person  addicted  to  the  use  of 
alcohol  is  also  less  likely  to  recover  from  the  disease  than 
one  who  has  avoided  its  use,  a  result  due  in  part  to  the 
weakening  effect  of  alcohol  upon  the  heart.  The  conges- 
tion of  the  lungs  in  pneumonia  makes  it  very  difficult  for 
the  heart  to  force  the  blood  through  them.  The  weakened 
heart  of  the  drunkard  gives  way  under  the  task. 

The  statement  sometimes  made  that  alcohol  is  beneficial 

1  Osier,  The  Principles  and  Practice  of  Medicine. 


RESPIRATION  99 

in  pulmonary  tuberculosis  is  without  foundation  in  fact. 
On  the  other  hand,  alcoholism  is  a  recognized  cause  of  con- 
sumption. Some  authorities  claim  that  this  disease  is  more 
frequent  in  heavy  drinkers  than  in  those  of  temperate 
habits,  in  the  proportion  of  about  three  to  one,  and  that 
possibly  half  of  the  cases  of  tuberculosis  are  traceable  to 
alcoholism.1 

The  Outdoor  Cure  for  Lung  Diseases.  —  Among  the  many  remedies 
proposed  for  consumption  and  kindred  diseases,  none  have  proved  more 
beneficial,  according  to  reports,  than  the  so-called  "  outdoor "  cure. 
The  person  having  consumption  is  fed  plentifully  upon  the  most  nour- 
ishing food,  and  is  made  to  spend  practically  his  entire  time,  including 
the  sleeping  hours,  out  of  doors.  Not  only  is  this  done  during  the 
pleasant  months  of  summer,  but  also  during  the  winter  when  the  tem- 
perature is  below  freezing.  Severe  exposure  is  prevented  by  overhead 
protection  at  night  and  by  sufficient  clothing  to  keep  the  body  warm. 
The  abundant  supply  of  pure,  cold  air  toughens  the  lungs  and  invigo- 
rates the  entire  body,  thereby  enabling  it  to  throw  off  the  disease. 

The  success  attending  this  method  of  treating  consumptives  suggests 
the  proper  mode  of  strengthening  lungs  that  are  not  diseased,  but  sim- 
ply weak.  The  person  having  weak  lungs  should  spend  as  much  time 
as  he  conveniently  can  out  of  doors.  He  should  provide  the  most  am- 
ple ventilation  at  night  and  have  a  sleeping  room  to  himself.  He 
should  practice  deep  breathing  exercises  and  partake  of  a  nourishing 
diet.  While  avoiding  prolonged  chilling  and  other  conditions  liable 
to  induce  colds,  he  should  take  advantage  of  every  opportunity  of  ex- 
posing himself  fully  and  freely  to  the  outside  atmosphere. 

Summary.  —  The  purpose  of  respiration  is  to  bring 
about  an  exchange  of  gases  between  the  body  and  the 
atmosphere.  The  organs  employed  for  this  purpose, 
called  the  respiratory  organs,  are  adapted  to  handling 
materials  in  the  gaseous  state,  and  are  operated  in  accord- 
ance with  principles  governing  the  movements  of  the 
atmosphere.  By  alternately  increasing  and  diminishing 

1  Huber,  Consumption  and  Civilization. 


100 


THE   VITAL   PROCESSES 


the  thoracic  space,  air  is  made  to  pass  between  the  outside 
atmosphere  and  the  interior  of  the  lungs.  Finding  its 
way  into  the  smallest  divisions  of  the  lungs,  called  the 
alveoli,  the  air  comes  very  near  a  large  surface  of  blood. 
By  this  means  the  carbon  dioxide  diffuses  out  of  the 
blood,  and  the  free  oxygen  enters.  Through  the  com- 
bined action  of  the  organs  of  respiration  and  the  organs 

that  move  the  blood  and  the 
lymph,  the  cells  in  all  parts  of 
the  body  are  enabled  to  exchange 
certain  gaseous  materials  with 
the  outside  atmosphere. 


FIG.  49.  —  Model  for  demonstrat- 
ing the  lungs. 


Exercises. —  I.  How  does  air  en- 
tering the  lungs  differ  in  composition 
from  air  leaving  the  lungs  ?  What 
purposes  of  respiration  are  indicated  by 
these  differences  ? 

2.  Name  the  divisions  of  the  lungs. 

3.  Trace  air  from  the  outside  at- 
mosphere into  the  alveoli.     Trace  the  blood  from  the  right  ventricle  to 
the  alveoli  and  back  again  to  the  left  auricle. 

4.  How  does  the  movement  of  air  into  and  from  the  lungs  differ 
from  that  of  the  blood  through  the  lungs  with  respect  to  (a)  the  direc- 
tion of  the  motion.  (<£)  the  causes  of  the  motion,  and  (V)  the  tubes 
through  which  the  motion  takes  place  ? 

5.  How  are  the  air  passages  kept  clean  and  open  ? 

6.  Describe  the  pleura.     Into  what  divisions  does  it  separate  the 
thoracic  cavity  ? 

7.  Describe  and  name  uses  of  the  diaphragm. 

8.  If  30  cubic  inches  of  air  are  passed  into  the  lungs  at  each 
inspiration  and  .05  of  this  is  retained  as  oxygen,  calculate  the  number 
of  cubic  feet  of  oxygen  consumed  each  day,  if  the  number  of  inspira- 
tions be  1 8  per  minute. 

9.  Find  the  weight  of  a  day's  supply  of  oxygen,  as  found  in  the 
above  problem,  allowing  1.3  ounces  as  the  weight  of  a  cubic  foot. 

10.   Make  a  study  of  the  hygienic  ventilation  of  the  schoolroom. 


RESPIRATION 


IOI 


ir.   Give  advantages  of  full  breathing  over  shallow  breathing. 

12.  How  may  a  flat  chest  and  round  shoulders  be  a  cause  of  con- 
sumption ?     How  may  these  deformities  be  corrected  ? 

13.  Give  general  directions  for  applying  artificial  respiration. 

PRACTICAL   WORK 

Examine  a  dissectible  model  of  the  chest  and  its  contents  (Fig.  49). 
Note  the  relative  size  of  the  two  lungs  and  their  position  with  reference 
to  the  heart  and  diaphragm.  Compare  the  side  to  side  and  vertical 
diameters  of  the  cavity.  Trace  the  air  tubes  from  the  trachea  to  their 
smallest  divisions. 

Observation  of  Lungs  (Optional).  —  Secure  from  a  butcher  the  lungs 
of  a  sheep,  calf,  or  hog.  The  windpipe  and  heart  should  be  left  attached 
and  the  specimen  kept  in  a  moist  condition  until  used.  Demonstrate 
the  trachea,  bronchi,  and  the  bronchial  tubes,  and  the  general  arrange- 
ment of  pulmonary  arteries  and  veins.  Examine  the  pleura  and  show 
lightness  of  lung  tissue  by  floating  a  piece  on  water. 

To  show  the  Changes  that  Air  undergoes  in  the  Lungs.  —  i .  Fill  a 
quart  jar  even  full  of  water.  Place  a  piece  of  cardboard  over  its  mouth 
and  invert,  without  spilling,  in  a  pan  of  water. 
Inserting  a  tube  under  the  jar,  blow  into  it 
air  that  has  been  held  as  long  as  possible 
in  the  lungs.  When  filled  with  air,  remove 
the  jar  from  the  pan,  keeping  the  top  well 
covered.  Slipping  the  cover  slightly  to  one 
side,  insert  a  burning  splinter  and  observe 
that  the  flame  is  extinguished.  This  proves 
the  absence  of  sufficient  oxygen  to  support 
combustion.  Pour  in  a  little  limewater1  and 
shake  to  mix  with  the  air.  The  change  of 
the  limewater  to  a  milky  white  color  proves 
the  presence  of  carbon  dioxide. 


FIG.  50.  —  Apparatus 
for  showing  changes  which 
air  undergoes  while  in  the 
lungs. 


2.  The  effects  illustrated  in  experiment  i  may  be  shown  in  a  some- 
what more  striking  manner  as  follows :  Fill  two  bottles  of  the  same 

1  To  prepare  Hmewater  some  small  lumps  of  fresh  lime  (either  slacked  or 
unslacked)  are  added  to  a  large  bottle  of  water  and  thoroughly  shaken.  This  is 
put  aside  until  the  lime  all  settles  to  the  bottom  and  the  water  above  is  perfectly 
clear.  This  is  now  ready  for  use  and  may  be  poured  off  as  needed.  When  the 
supply  is  exhausted  add  more  water  and  shake  again. 


I02  THE   VITAL  PROCESSES 

size  each  one  fourth  full  of  limewater  and  fit  each  with  a  two-holed  rubber 
stopper  (Fig.  50).  Fit  into  each  stopper  one  short  and  one  long  glass 
tube,  the  long  tube  extending  below  the  limewater.  Connect  the 
short  tube  of  one  bottle  and  the  long  tube  of  the  other  bottle  with 
a  Y-tube.  Now  breathe  slowly  three  or  four  times  through  the  Y-tube. 
It  will  be  found  that  the  inspired  air  passes  through  one  bottle  and  the 
expired  air  through  the  other.  Compare  the  effect  upon  the  lime- 
water  in  the  two  bottles.  Insert  a  small  burning  splinter  into  the  top 
of  each  bottle  and  note  result.  What  differences  between  inspired  and 
expired  air  are  thus  shown? 

3.  Blow  the  breath  against  a  cold  window  pane.     Note  and  account 
for  the  collection  of  moisture. 

4.  Note  the  temperature  of  the  room  as  shown  by  a  thermometer. 
Now  breathe  several  times  upon  the  bulb,  noting  the  rise  in  the  mer- 
cury.    What  does  this  experiment  show  the  body  to  be  losing  through 
the  breath? 

To  show  Changes  in  the  Thoracic  Cavity.  —  i.   To  a  yard-  or  meter- 
stick,  attach  two  vertical  strips,  each  about  eight  inches  long,  as  shown 


FIG.  51. — Apparatus  for  measuring  chest  expansion. 

in  Fig.  51.  The  piece  at  the  end  should  be  secured  firmly  in  place 
by  screws  or  nails.  The  other  should  be  movable.  With  this  con- 
trivance measure  the  sideward  and  forward  expansion  of  a  boy's  thorax. 
Take  the  diameter  first  during  a  complete  inspiration  and  then  during 
a  complete  expiration,  reading  the  difference.  Compare  the  forward 
with  the  sideward  expansion. 

2.  With  a  tape-line  take  the  circumference  of  the  chest  when  all 
the  air  possible  has  been  expelled  from  the  lungs.  Take  it  again  when 
the  lungs  have  been  fully  inflated.  The  difference  is  now  read  as  the 
chest  expansion. 

To  illustrate  the  Action  of  the  Diaphragm.  —  Remove  the  bottom 
from  a  large  bottle  having  a  small  neck.  (Scratch  a  deep  mark  with  a 


RESPIRATION 


103 


file  and  hold  on  the  end  of  this  mark  a  hot  poker.  When  the  glass 
cracks,  lead  the  crack  around  the  bottle  by  heating  about  one  half  inch 
in  advance  of  it.)  Place  the  bottle  in  a  large  glass  jar  filled  two  thirds 
full  of  water  (Fig.  52).  Let  the  space  above 
the  water  represent  the  chest  cavity  and 
the  water  surface  represent  the  diaphragm. 
Raise  the  bottle,  noting  that  the  water  falls, 
thereby  increasing  the  space  and  causing  air 
to  enter.  Then  lower  the  bottle,  noting  the 
opposite  effect.  To  show  the  movement  of 
the  air  in  and  out  ot  the  bottle,  hold  with 
the  hand  (or  arrange  a  support  for)  a  burn- 
ing splinter  over  the  mouth  of  the  bottle. 

To  estimate  the  Capacity  of  the  Lungs.  — 
Breathing  as  naturally  as  possible,  expel  the 
air  into  a  spirometer  (lung  tester)  during  a 
period,  say  of  ten  respirations  (Fig.  53). 


FIG.  52.  —  Simple  appa- 
ratus for  illustrating  the 
action  of  the  diaphragm. 


Note  the  total  amount  of 
air  exhaled  and  the  number  of  "  breaths  "  and  calculate  the  amount  of 

air  exhaled  at  each  breath.    This 
is  called  the  tidal  air. 

2.  After  an  ordinary  inspira- 
tion empty  the  lungs  as  com- 
pletely as  possible  into  the  spi- 
rometer, noting  the  quantity 
exhaled.  This  amount,  less  the 
tidal  air,  is  known  as  the  reserve 
air.  The  air  which  is  now  left 
in  the  lungs  is  called  the  residual 
air.  On  the  theory  that  this  is 
equal  in  amount  to  the  reserve 
air,  calculate  the  capacity  of  the 
lungs  in  an  ordinary  inspiration. 


FIG.  53.  —  Apparatus  (spirometer)  for 
measuring  the  capacity  of  the  lungs. 


3.  Now  fill  the  lungs  to  the  full  expansion  of  the  chest  and  empty 
them  as  completely  as  possible  into  the  spirometer,  noting  the  amount 
expelled.  This,  less  the  tidal  air  and  the  reserve  air,  is  called  the  com- 
plemental  air.  Now  calculate  the  total  capacity  of  the  lungs. 


CHAPTER  VIII 
PASSAGE  OF  OXYGEN  THROUGH  THE  BODY 

WHAT  is  the  nature  of  oxygen  ?  What  is  its  purpose  in 
the  body  and  how  does  it  serve  this  purpose  ?  How  is  the 
blood  able  to  take  it  up  at  the  lungs  and  give  it  off  at  the 
cells  ?  What  becomes  of  it  after  being  used  ?  These  are 
questions  touching  the  maintenance  of  life  and  they 
deserve  careful  consideration. 

Nature  of  Oxygen.  —  To  understand  the  relation  which 
oxygen  sustains  to  the  body  we  must  acquaint  ourselves 
with  certain  of  its  chemical  properties.  It  is  an  element1 
of  intense  affinity,  or  combining  power,  and  is  one  of  the 
most  active  of  all  chemical  agents.  It  is  able  to  com- 
bine with  most  of  the  other  elements  to  form  chemical 
compounds.  A  familiar  example  of  its  combining  action 
is  found  in  ordinary  combustion,  or  burning.  On  account 
of  the  part  it  plays  in  this  process,  oxygen  is  called  the 
supporter  of  combustion ;  but  it  supports  combustion  by 
the  simple  method  of  uniting.  The  ashes  that  are  left  and 
the  invisible  gases  that  escape  into  the  atmosphere  are 
the  compounds  formed  by  the  uniting  process.  It  thus 
appears  that  oxygen,  in  common  with  the  other  elements, 
may  exist  in  either  of  two  forms  : 

1  An  element  is  a  single  kind  of  matter.  Those  substances  are  classed  as 
elements  which  cannot  be  separated  into  different  kinds  of  matter.  Two  or 
more  elements  combined  in  definite  proportions  by  weight  form  a  compound. 
The  elements  are  few  in  number,  only  about  eighty  being  known.  Compounds, 
on  the  other  hand,  are  exceedingly  numerous. 

104 


PASSAGE   OF    OXYGEN    THROUGH    THE    BODY     105 

1.  That  in  which  it  is  in  a  free,  or  uncombined,  condi- 
tion —  the  form  in  which  it  exists  in  the  atmosphere. 

2.  That  in  which  it  is  a  part  of  compounds,  such  as  the 
compounds  formed  in  combustion. 

Oxygen  manifests  its  activity  to  the  best  advantage 
when  it  is  in  a  free  state,  or,  more  accurately  speaking, 
when  it  is  passing  from  the  free  state  into  one  of  combina- 
tion. It  is  separated  from  its  compounds  and  brought 
again  into  a  free  state  by  overcoming  with  heat,  or  some 
other  force,  the  affinity  which  causes  it  to  unite. 

How  Oxygen  unites. — The  chemist  believes  oxygen,  as 
well  as  all  other  substances,  to  be  made  up  of  exceedingly 
small  particles,  called  atoms.  The  atoms  do  not  exist 
singly  in  either  elements  or  compounds,  but  are  united 
with  each  other  to  form  groups  of  atoms  that  are  called 
molecules.  In  an  element  the  molecules  are  made  up  of 
one  kind  of  atoms,  but  in  a  compound  the  molecules  are 
made  up  of  as  many  kinds  of  atoms  as  there  are  elements 
in  the  compound.  Changes  in  the  composition  of  sub- 
stances (called  chemical  changes)  are  due  to  rearrange- 
ments of  the  atoms  and  the  formation  of  new  molecules. 
The  atoms,  therefore,  are  the  units  of  chemical  combina- 
tion. In  the  formation  of  new  compounds  they  unite,  and 
in  the  breaking  up  of  existing  compounds  they  separate. 

The  uniting  of  oxygen  is  no  exception  to  this  general 
law.  All  of  its  combinations  are  brought  about  by  the 
uniting  of  its  atoms.  In  the  burning  of  carbon,  for  .exam- 
ple, the  atoms  of  oxygen  and  the  atoms  of  carbon  unite, 
forming  molecules  of  the  compound  known  as  carbon 
dioxide.  The  chemical  formula  of  this  compound,  which 
is  CO2,  shows  the  proportion  in  which  the  atoms  unite  — 
one  atom  of  carbon  uniting  with  two  atoms  of  oxygen  in 
each  of  the  molecules.  The  affinity  of  oxygen  for  other 


I06  THE   VITAL   PROCESSES 

elements,  and  the  affinity  of  other  elements  for  oxygen, 
and  for  each  other,  resides  in  their  atoms. 

Oxidation.  —  The  uniting  of  oxygen  with  other  elements 
is  termed  oxidation.  This  may  take  place  slowly  or 
rapidly,  the  two  rates  being  designated  as  slow  oxidation 
and  rapid  oxidation.  Examples  of  slow  oxidation  are 
found  in  certain  kinds  of  decay  and  in  the  rusting  of  iron. 
Combustion  is  an  example  of  rapid  oxidation.  Slow  and 
rapid  oxidation,  while  differing  widely  in  their  effects  upon 
surrounding  objects,  are  alike  in  that  both  produce  heat 
and  form  compounds  of  oxygen.  In  slow  oxidation,  how- 
ever, the  heat  may  come  off  so  gradually  that  it  is  not 
observed. 

Movement  of  Oxygen  through  the  Body.  —  Oxygen  has 
been  shown  in  the  preceding  chapters  to  pass  from  the 
lungs  into  the  blood  and  later  to  leave  the  blood  and,  pass- 
ing through  the  lymph,  to  enter  the  cells.  That  oxygen 
does  not  become  a  permanent  constituent  of  the  cells  is 
shown  by  the  constancy  of  the  body  weight.  Nearly  two 
pounds  of  oxygen  per  day  are  known  to  enter  the  cells  of 
the  average-sized  person.  If  this  became  a  permanent 
part  of  the  cells,  the  body  would  increase  in  weight  from 
day  to  day.  Since  the  body  weight  remains  constant,  or 
nearly  so,  we  must  conclude  that  oxygen  leaves  the  body 
about  as  fast  as  it  enters.  Oxygen  enters  the  body  as  a 
free  element.  The  form  in  which  it  leaves  the  body  will 
be  understood  when  we  realize  the  purpose  which  it  serves 
and  the  method  by  which  it  serves  this  purpose. 

Purpose  of  Oxygen  in  the  Body.  —  The  question  may  be 
raised :  Is  it  possible  for  oxygen  to  serve  a  purpose  in  the 
body  without  remaining  in  it?  This,  of  course,  depends 
upon  what  the  purpose  is.  That  it  is  possible  for  oxygen 
to  serve  a  purpose  and  at  the  same  time  pass  on  through 


PASSAGE    OF    OXYGEN    THROUGH    THE    BODY     107 


the  place  where  it  serves  that  purpose,  is  seen  by  studying 
the  combustion  in  an  ordinary  stove  (Fig.  54).  Oxygen 
enters  at  the  draft  and  for  the 
most  part  passes  out  at  the  flue, 
but  in  passing  through  the  stove 
it  unites  with,  or  oxidizes,  the  fuel, 
causing  the  combustion  which  pro- 
duces the  heat. 

Now  it  is  found  that  certain 
chemical  processes,  mainly  oxida- 
tions, are  taking  place  in  the  body. 
These  produce  the  heat  for  keep- 
ing it  warm  and  also  supply  other 
forms  of  energy,1  including  motion. 
It  is  the  purpose  of  oxygen  to  keep 
up  these  oxidations  and,  by  so 
doing,  to  aid  in  supplying  the  body 
with  energy.  It  serves  this  pur- 


w\v 


FIG.   54. — Coal  stove  illus- 
trating rapid  oxidation. 


pose  in  much  the  same  way  that  it  supports  combustion, 
i.e.,  by  uniting  with,  or  oxidizing,  materials  derived  from 
foods  that  are  present  in  the  cells. 

Does  Oxygen  serve  Other  Purposes  ?  —  It  has  been  sug- 
gested that  oxygen  may  serve  the  purpose  of  oxidizing,  or 
destroying,  substances  that  are  injurious  and  of  acting,  in 
this  way,  as  a  purifying  agent  in  the  body.  In  support  of 
this  viev/  is  the  natural  tendency  of  oxygen  to  unite  with 
substances  and  the  well-known  fact  that  oxygen  is  an  im- 
portant natural  agent  in  purifying  water.  It  seems  prob- 
able, therefore,  that  it  may  to  a  slight  extent  serve  this 
purpose  in  the  body.  It  is  probable  also  that  oxygen  aids 
through  its  chemical  activity  in  the  formation  of  compounds 

1  The  term  energy,  as  used  here,  has  the  same  general  meaning  as  the  word 
power.  See  Chapter  XII. 


I08  THE   VITAL   PROCESSES 

which  are  to  become  a  part  of  the  cells.  Both  of  these 
uses,  however,  are  of  minor  importance  when  compared 
with  the  main  use  of  oxygen,  which  is  that  of  an  aid  in  sup- 
plying energy  to  the  body. 

Oxygen  and  the  Maintenance  of  Life.  —  In  the  supplying 
of  energy  to  the  body,  one  of  the  conditions  necessary  to 
the  maintenance  of  life  is  provided.  Because  oxygen  is 
necessary  to  this  process,  and  because  death  quickly  results 
when  the  supply  of  it  is  cut  off,  oxygen  is  frequently  called 
the  supporter  of  life.  This  idea  is  misleading,  for  oxygen 
has  no  more  to  do  with  the  maintenance  of  life  than  have 
the  food  materials  with  which  it  unites.  Life  appears  to 
be  more  dependent  upon  oxygen  than  upon  food,  simply 
because  the  supply  of  it  in  the  body  at  any  time  is  exceed- 
ingly small.  Being  continually  surrounded  by  an  atmos- 
phere containing  free  oxygen,  the  body  depends  upon  this 
as  a  constant  source  of  supply,  and  does  not  store  it  up. 
Food,  on  the  other  hand,  is  taken  in  excess  of  the  body's 
needs  and  stored  in  the  various  tissues,  the  supply  being 
sufficient  to  last  for  several  days.  When  the  supply  of 
either  oxygen  or  food  is  exhausted  in  the  body,  life  must 
cease. 

The  Oxygen  Movement  a  Necessity.  —  Since  free  oxygen 
is  required  for  keeping  up  the  chemical  changes  in  the 
cells,  and  since  it  ceases  to  be  free  as  soon  as  it  goes  into 
combination,  its  continuous  movement  through  the  body  is 
a  necessity.  The  oxygen  compounds  must  be  removed  as 
fast  as  formed  in  order  to  make  room  for  more  free  oxygen. 
This  movement  has  already  been  studied  in  connection 
with  the  blood  and  the  organs  of  respiration,  but  the  con- 
sideration of  certain  details  has  been  deferred  till  now. 
By  what  means  and  in  what  form  is  the  oxygen  passed  to 
and  from  the  cells? 


PASSAGE   OF    OXYGEN    THROUGH    THE    BODY     109 

Passage  of  Oxygen  through  the  Blood.  —  In  serving  its 
purpose  at  the  cells,  the  oxygen  passes  twice  through  the 
blood  —  once  as  it  goes  toward  the  cells  and  again  as  it 
passes  from  the  cells  to  the  exterior  of  the  body  : 

Passage  toward  the  Cells.  —  This  is  effected  mainly 
through  the  hemoglobin  of  the  red  corpuscles.  At  the 
lungs  the  oxygen  and  the  hemoglobin  form  a  weak  chemi- 
cal compound  that  breaks  up  and  liberates  the  oxygen  when 
it  reaches  the  capillaries  in  the  tissues.  The  separation 
of  the  oxygen  from  the  hemoglobin  at  the  tissues  appears 
to  be  due  to  two  causes  :  first,  to  the  weakness  of  the 
chemical  attraction  between  the  atoms  of  oxygen  and  the 
atoms  that  make  up  the  hemoglobin  molecule  ;  and  second, 
to  a  difference  in  the  so-called  oxygeti  pressure  at  the  lungs 
and  at  the  tissues.1 

The  attraction  of  the  oxygen  and  the  hemoglobin  is  suf- 
ficient to  cause  them  to  unite  where  the  oxygen  pressure  is 
more  than  one  half  pound  to  the  square  inch,  but  it  is  not 
sufficiently  strong  to  cause  them  to  unite  or  to  prevent 
their  separation,  if  already  united,  where  the  oxygen  pres- 
sure is  less  than  one  half  pound  to  the  square  inch.  The 
oxygen  pressure  at  the  lungs,  which  amounts  to  nearly 
three  pounds  to  the  square  inch,  easily  causes  the  oxygen 
and  the  hemoglobin  to  unite,  while  the  almost  complete 
absence  of  any  oxygen  pressure  at  the  tissues,  permits 
their  separation.  The  blood  in  its  circulation  constantly 
flows  from  the  place  of  high  oxygen  pressure  at  the  lungs 

1  The  oxygen  pressure  of  the  atmosphere  is  that  portion  of  the  total  atmospheric 
pressure  which  is  due  to  the  weight  of  the  oxygen.  Since  oxygen  comprises  about 
one  fifth  of  the  atmosphere,  the  pressure  which  it  exerts  is  about  one  fifth  of  the 
total  atmospheric  pressure,  or,  at  the  sea  level,  about  three  pounds  to  the 
square  inch  (15  X  \  =  3) .  This  is  the  oxygen  pressure  of  the  atmosphere.  The  low 
oxygen  pressure  in  the  tissues  is  due  to  its  scarcity,  and  this  scarcity  is  due  to  its 
entering  into  combination  at  the  cells. 


I  IO 


THE   VITAL   PROCESSES 


to  the  place  of  low  oxygen  pressure  at  the  tissues  and,  in  so 
doing,  loads  up  with  oxygen  at  one  place  and  unloads  it  at 
the  other  (Fig.  55). 

Passage  front  the  Cells.  —  Since  oxygen  leaves  the  free 
state  at  the  cells  and  becomes  a  part  of  compounds,  we  are 
able  to  trace  it  from  the  body  only  by  following  the  course 


Carbon  cfioxitf* 
press  urf  tot" 


Oxygen  pressure 


FIG.  55.  —  Diagram  illustrating  movement  of  oxygen  and  carbon 
dioxide  through  the  body  (S.  D.  Magers).  Each  moves  from  a  place 
of  relatively  high  to  a  place  of  relatively  low  pressure.  (See  text.) 

of  these  compounds.  Three  waste  compounds  of  impor- 
tance are  formed  at  the  cells  —  carbon  dioxide  (CO2),  water 
(H2O),  and  urea  (N2H4CO).  The  first  is  formed  by  the 
union  of  oxygen  with  carbon,  the  second  by  its  union  with 
hydrogen,  and  the  third  by  its  union  with  nitrogen,  hydro- 
gen, and  carbon.  These  compounds  are  carried  by  the 
blood  to  the  organs  of  excretion,  where  they  are  removed 
from  the  body.  The  water  leaves  the  body  chiefly  as  a 
liquid,  the  urea  as  a  solid  dissolved  in  water,  and  the  car- 
bon dioxide  as  a  gas.  The  passage  of  carbon  dioxide 
through  the  blood  requires  special  consideration. 

Passage  of  Carbon  Dioxide  through  the  Blood.  —  Part  of 
the  carbon  dioxide  is  dissolved  in  the  plasma  of  the  blood, 
and  part  of  it  is  in  weak  chemical  combination  with  sub- 
stances found  in  the  plasma  and  in  the  corpuscles.  Its 
passage  through  the  blood  is  accounted  for  in  the  same 


PASSAGE   OF   OXYGEN   THROUGH   THE    BODY     ill 


way  as  the  passage  of  the  oxygen.  Its  ability  to  dissolve 
in  liquids  and  to  enter  into  chemical  combination  varies  as 
the  carbon  dioxide  pressure!  This  in  turn  varies  with  the 
amount  of  the  carbon  dioxide,  which  is  greatest  at  the  cells 
(where  it  is  formed),  less  in  the  blood,  and  still  less  in  the 
lungs.  Because  of  these  differences,  the  blood  is  able  to 
take  it  up  at  the  cells  and  release  it  at  the  lungs  (Fig.  55). 
Properties  of  Carbon  Dioxide.  —  Carbon  dioxide  is  a  color- 
less gas  with  little  or  no  odor.  It  is  classed  as  a  heavy 
gas,  being  about  one  third  heavier  than  air2  (Fig.  56). 
It  does  not  support  combustion,  but  on  the  contrary  is 
used  to  some  extent  to  extinguish  fires. 
It  is  formed  by  the  oxidation  of  carbon 
in  the  body,  and  by  the  combustion  of 
carbon  outside  of  the  body.  It  is  also 
formed  by  the  decay  of  animal  and  veg- 
etable matter.  From  these  sources  it 

FIG.     56.  —  Soap 

is  continually  finding  its  way  into  the  bubble  floating  in  a 
atmosphere.  Although  not  a  poisonous  vessel  of  carbon  diox- 
gas,  carbon  dioxide  may,  if  it  surround  ide>  illustrating  the 

, ,       i      i         i  ,   ,  i  i        r  difference    in    weight 

the  body,  shut  out  the  supply  of  oxygen   ,  • 

J  rr  j  jo  between   air   and    car- 

and  cause  death.3 


Carbon 
dioxide 


between  air  and   car- 
bon dioxide  gas. 


1  See  footnote  on  oxygen  pressure,  page  109. 

2  The  impression  prevails  to  some  extent  that  carbon  dioxide,  on  account  of  its 
weight,  settles  out  of  the  atmosphere,  collecting  in  old  wells  and  at  the  floor  in 
crowded  rooms.    Any  such  settling  of  the  carbon  dioxide  is  prevented  by  the  rapid 
motion  of  its  molecules.     This  motion  not  only  prevents  a  separation  of  carbon 
dioxide  and  air  after  they  are  mixed,  but  causes  them  to  mix  rapidly  when  they  are 
separated,  if  they  still  have  surface  contact.     The  carbon  dioxide  found  in  old  wells 
is  formed  there  by  decaying  vegetable  or  animal  matter.     In  rooms  it  is  no  more 
abundant  at  the  floor  than  in  other  parts. 

3  On  account  of  the  formation  of  carbon  dioxide  in  places  containing  decaying 
material,  the  descent  into  an  old  well  or  other  opening  into  the  earth  is  often  a 
hazardous  undertaking.     Before  making  such  a  descent  the  air  should  always  be 
tested  by  lowering  a  lighted  lantern  or  candle.    Artificial  respiration  is  the  only 
means  of  restoring  one  who  has  been  overcome  by  this  gas  (page  97). 


112 


THE   VITAL   PROCESSES 


Final  Disposition  of  Carbon  Dioxide.  —  It  is  readily  seen 
that  the  union  of  carbon  and  oxygen,  which  is  continually 
removing  oxygen  from  the  air  and  replacing  it  with  carbon 
dioxide,  tends  to  make  the  whole  atmosphere  deficient  in 
the  one  and  to  have  an  excess  of  the  other.  This  tendency 
is  counteracted  through  the  agency  of  vegetation.  Green 
plants  absorb  the  carbon  dioxide  from  the  air,  decompose 
it,  build  the  carbon  into  compounds  (starch,  etc.)  that 
become  a  part  of  the  plant,  and  return  the  free  oxygen  to 
the  air  (Fig.  57).  In  doing  this,  they  not  only  preserve  the 
necessary  proportion  of  oxygen  and  carbon  dioxide  in  the 
atmosphere,  but  also  put  the  carbon  and  oxygen  in  such  a 
condition  that  they  can  again  unite.  The  force  which 

enables  the  plant  cells  to  decom- 
pose the  carbon  dioxide  is  sup- 
plied by  the  sunlight  (Chapter 
XII). 

Summary.  —  Oxygen,  by  unit- 
ing with  materials  at  the  cells, 
keeps  up  a  condition  of  chemical 
activity  (oxidation)  in  the  body. 
This  supplies  heat  and  the  other 
forms  of  bodily  energy.  Enter- 


Fiu.  57.  — Under  surface  of  a  ing   as   a   free   element,    oxygen 
geranium  leaf  showing  breathing   ^^  ^  ^      ^  &  Q£  the 

pores,  highly  magnified  (O.  H.).  •*  . 

waste  compounds  which  it  helps 

to  form.  The  free  oxygen  is  transported  from  the  lungs 
to  the  cells  by  means  of  the  hemoglobin  of  the  red  cor- 
puscles, while  the  combined  oxygen  in  carbon  dioxide  and 
other  compounds  from  the  cells  is  carried  mainly  by  the 
plasma.  The  limited  supply  of  free  oxygen  in  the  body 
at  any  time  makes  necessary  its  continuous  introduction 
into  the  body. 


PASSAGE   OF   OXYGEN   THROUGH   THE    BODY     113 

Exercises. —  i.  Describe  the  properties  of  oxygen.  How  does  it 
unite  with  other  elements?  How  does  it  support  combustion? 

2.  State  the   purpose  of  oxygen   in   the   body.     What  properties 
enable  it  to  fulfill  this  purpose? 

3.  What  is  the  proof  that  oxygen  does  not  remain  permanently  in 
the  body?     How  does  the  oxygen  entering  the  body  differ  from  the 
same  oxygen  as  it  leaves  the  body? 

4.  What  is  the  necessity  for  the  continuous  introduction  of  oxygen 
into  the  body,  while  food  is  introduced  only  at  intervals  ? 

5.  How  are  the  red  corpuscles  able  to  take  up  and  give  off  oxygen? 
How  is  the  plasma  able  to  take  up  and  give  off  carbon  dioxide? 

6.  If  thirty  cubic  inches  of  air  pass  from  the  lungs  at  each  expiration 
and  4.5  per  cent  of  this  is  carbon  dioxide,  calculate  the  number  of  cubic 
feet  of  the  gas  expelled  in  twenty-four  hours,  estimating  the  number  of 
respirations  at  eighteen  per  minute. 

7.  What  is  the  weight  of  this  volume  of  carbon  dioxide,  if  one  cubic 
foot  weigh  1.79  ounces? 

8.  What  portion  of  this  weight  is  oxygen  and  what  carbon,  the  ratio 
by  weight  of  carbon  to  oxygen  in  carbon  dioxide  being  twelve  to  thirty- 
two? 

9.  What  is  the  final  disposition  of  carbon  dioxide  in  the  atmos- 
phere? 

PRACTICAL  WORK 

To  show  the  Difference  between  Free  Oxygen  and  Oxygen  in  Com- 
bination.—  Examine  some  crystals  of  potassium  chlorate  .(KC1O3). 
They  contain  oxygen  in  combination  with  potassium  and  chlorine. 
Place  a  few  of  these  in  a  small  test  tube  and  heat  strongly  in  a  gas  or 
alcohol  flame.  The  crystals  first  melt,  and  the  liquid  which  they  form 
soon  appears  to  boil.  If  a  splinter,  having  a  spark  on  the  end,  is  now 
inserted  in  the  tube,  it  is  kindled  into  a  flame.  This  shows  the  presence 
of  free  oxygen,  the  heat  having  caused  the  potassium  chlorate  to  decom- 
pose. The  difference  between  free  and  combined  oxygen  may  also  be 
shown  by  decomposing  other  compounds  of  oxygen,  such  as  water  and 
mercuric  oxide. 

Preparation  and  Properties  of  Oxygen.  —  Intimately  mix  3  grams 
(\  teaspoonful)  of  potassium  chlorate  with  half  its  bulk  of  manganese 
dioxide,  and  place  the  mixture  in  a  large  test  tube.  Close  the  test 
tube  with  a  tight-fitting  stopper  which  bears  a  glass  tube  of  sufficient 


114 


THE   VITAL   PROCESSES 


length  and  of  the  right  shape  to  convey  the  escaping  gas  to  a  small 
trough  or  pan  partly  filled  with  water,  on  the  table.  Fill  four  large- 
mouthed  bottles  with  water  and,  by  covering  with  cardboard,  invert 
each  in  the  trough  of  water.  Arrange  the  test  tube  conveniently  for 


FIG.  58.  —  Apparatus  for  generating  oxygen. 

heating,  letting  the  end  of  the  glass  tube  terminate  under  the  mouth  of 
one  of  the  bottles  (Fig.  58).  Using  an  alcohol  lamp  or  a  Bunsen 
burner,  heat  over  the  greater  portion  of  the  tube  at  first,  but  gradually 
concentrate  the  flame  upon  the  mixture.  Do  not  heat  too  strongly,  and 
when  the  gas  is  coming  off  rapidly,  remove  the  flame  entirely,  putting  it 
back  as  the  action  slows  down.  After  all  the  bottles  have  been  filled, 
remove  the  end  of  the  glass  tube  from  the  'water,  but  leave  the  bottles 
of  oxygen  inverted  in  the  trough  until  they  are  to  be  used.  On  remov- 
ing the  bottles  from  the  trough,  keep  the  tops  covered  with  wet  card- 
board. 

1.  Examine  a  bottle  of  oxygen,  noting  its  lack  of  color.     Insert  a 
small  burning  splinter  in  the  upper  part  of  the  bottle  and  observe  the 
change  in  the  rate  of  burning.     The  air  contains  free  oxygen,  but  it  is 
diluted  with  nitrogen.     Compare  this  with  the  undiluted  oxygen  in  the 
bottle  as  to  effect  in  causing  the  splinter  to  burn. 

2.  In  a  second  bottle  of  oxygen  insert  a  splinter  without  the  flame, 
but  having  a  small  spark  on  the  end.     As  soon  as  the  oxygen  kindles 
the  spark  into  a  flame,  withdraw  from  the  bottle  and  blow  out  the  flame, 
but  again  insert  the  spark.     Repeat  the  experiment  as  long  as  the  spark 
is  kindled  by  the  oxygen  into  a  flame.     This  experiment  is  usually  per- 
formed as  a  test  for  undiluted  oxygen. 

3.  Make  a  hollow  cavity  in  the  end  of  a  short  piece  of  crayon. 
Fasten  a  wire  to  the  crayon,  and  fill  the  cavity  with  powdered  sulphur. 


PASSAGE   OF   OXYGEN   THROUGH    THE   BODY     115 

Ignite  the  sulphur  in  the  flame  of  an  alcohol  lamp  or  Bunsen  burner, 
and  lower  it  into  a  bottle  of  oxygen.  Observe  the  change  in  the  rate 
of  burning,  the  color  of  the  flame,  and  the  material  formed  in  the  bottle 
by  the  burning.  The  gas  remaining  in  the  bottle  is  sulphur  dioxide 
(SO2),  formed  by  the  uniting  of  the  sulphur  and  the  oxygen. 

4.  Bend  a  small  loop  on*  the  end  of  a  piece  of  picture  wire.  Heat  the 
loop  in  a  flame  and  insert  it  in  some  powdered  sulphur.  Ignite  the 
melted  sulphur  which  adheres,  and  insert  it  quickly  in  a  bottle  of  oxygen. 
Observe  the  dark,  brittle  material  which  is  formed  by  the  burning  of  the 
iron.  It  is  a  compound  of  the  iron  with  oxygen,  similar  to  iron  rust,  and 
formed  by  their  uniting. 

Preparation  and  Properties  of  Carbon  Dioxide.  —  I.  (a)  Attach  a 
piece  of  carbon  (charcoal)  no  larger  than  the  end  of  the  thumb  to  a  piece 
of  wire.  Ignite  the  charcoal  in  a  hot  flame  and  lower  it  into  a  vessel  of 
oxygen.  Observe  its  combustion,  letting  it  remain  in  the  bottle  until  it 
ceases  to  burn.  Note  that  the  burning  has  consumed  a  part  of  the  car- 
bon and  has  used  up  the  free  oxygen.  Has  anything  been  formed  in 
their  stead? 

(b)  Remove  the  charcoal  and  add  a  little   limewater.     Cover  the 
bottle  with  a  piece  of  cardboard,  and  bring  the  gas  and  the  limewater 
in  contact  by  shaking.     Note  any  change  in  the  color  of  the  limewater. 
If  it  turns  white,  the  presence  of  carbon  dioxide  is  proved. 

•2..  Burn  a  splinter  in  a  large  vessel  of  air,  keeping  the  top  covered. 
Add  limewater  and  shake.  Note  and  account  for  the  result. 

3.  Place  several  pieces  of  marble  (limestone)  in  a  jar  holding  at  least 
half  a  gallon.  Barely  cover  the  marble  with  water,  and  then  add  hydro- 
chloric acid  until  a  gas  is  rapidly  evolved.  This  gas  is  carbon  dioxide. 

(«)    Does  it  possess  color? 

(V)    Insert  a  burning  splinter  to  see  if  it  supports  combustion. 

(c)  Place  a  bottle  of  oxygen  by  the  side  of  the  vessel  of  carbon  di- 
oxide.    Light  a  splinter  and  extinguish  the  flame  by  lowering  it  into 
the  vessel  of  carbon  dioxide.     Withdraw  immediately,  and  if  a  spark 
remains  on  the  splinter,  thrust  it  into  the  bottle  of  oxygen.     Then  in- 
sert the  relighted  splinter  into  the  carbon  dioxide.      Repeat  several 
times,  kindling  the  flame  in  one  gas  and  extinguishing  it  in  the  other. 
Finally  show  that  the  spark  also  may  be  extinguished  by  holding  the 
splinter  a  little  longer  in  the  carbon  dioxide. 

(</)  Tip  the  jar  containing  the  carbon  dioxide  over  the  mouth  of  a 
tumbler,  as  in  pouring  water,  though  not  far  enough  to  spill  the  acid,  and 


THE   VITAL    PROCESSES 


Carbon 


then  insert  a  burning  splinter  in  the  tumbler.     Account  for  the  result. 
Inference  as  to  the  weight  of  carbon  dioxide. 

(e)    Review  experiments  (page    101)   showing 
the  presence  of  carbon  dioxide  in  the  breath. 

To  illustrate  the  General  Movement  of  Oxygen 
through  the  Body.  — Into  a  glass  tube,  six  inches 
in  length  and  open  at  both   ends,  place  several 
small  lumps  of  charcoal  (Fig.  59).     Fit  into  one 
end  of  this  tube,  by  means  of  a  stopper,  a  smaller 
glass  tube  which  is  bent  at  right  angles  and  which 
FIG  59  —Simple  is  made  to  ^>ass  throu§h  a  close-fitting  stopper  to 
apparatus  for   illus-  ^e   bottom   of  a  small   bottle.      Another  small 
is  fitted  into  a  second  hole  in  this  stopper, 


trating  passage  of  oxy- 
gen  through  the  body.  but  terminating  near  the  top  of  the  bottle,  and  to 
this  is  connected  a  rubber  tube  about  eighteen 
inches  in  length.  The  arrangement  is  now  such  that  by  sucking  air 
from  the  top  of  the  bottle,  it  is  made  to  enter  at  the  distant  end  of  the 
tube  containing  the  charcoal.  After  filling  the  bottle  one  third  full 
of  limewater,  heat  the  tube  containing  the  charcoal  until  it  begins  to 
glow.  Then  suck  the  air  through  the  apparatus  (as  in  smoking,  without 
drawing  it  into  the  lungs),  observing  what  happens  both  in  the  tube 
and  in  the  bottle.  What  are  the  proofs  that  the  oxygen,  in  passing 
through  the  tube,  unites  with  the  carbon,  forms  carbon  dioxide,  and 
liberates  energy?  Compare  the  changes  which  the  oxygen  undergoes 
while  passing  through  the  tube  with  the  changes  which  it  undergoes  in 
passing  through  the  body. 


CHAPTER   IX 
FOODS  AND   THE   THEORY  OF  DIGESTION 

THE  body  is  constantly  in  need  of  new  material.  Oxi- 
dation, as  shown  in  the  preceding  chapter,  rapidly  destroys 
substances  at  the  cells,  and  these  have  to  be  replaced.  Upon 
this  renewal  depends  the  supply  of  energy.  Moreover, 
there  is  found  to  be  an  actual  breaking  down  of  the  living 
material,  or  protoplasm,  in  the  body.  While  this  does  not 
destroy  the  cells,  as  is  sometimes  erroneously  stated,  it 
reduces  the  quantity  of  the  protoplasm  and  makes  neces- 
sary a  process  of  repair,  or  rebuilding,  of  the  tissues.  This 
also  requires  new  material.  Finally,  substances,  such  as 
water  and  common  salt,  are  required  for  the  aid  which  they 
render  in  the  general  work  of  the  body.  Since  these  are 
constantly  being  lost  in  one  way  or  another,  they  also  must 
be  replaced.  These  different  needs  of  the  body  for  new 
materials  are  supplied  through 

The  Foods.  —  Foods  are  substances  that,  on  being  taken 
into  the  healthy  body,  are  of  assistance  in  carrying  on  its 
work.  This  definition  properly  includes  oxygen,  but  the 
term  is  usually  limited  to  substances  introduced  through 
the  digestive  organs.  As  suggested  above,  foods  serve 
at  least  three  purposes : 

1.  They,  with  oxygen,  supply  the  body  with  energy. 

2.  They  provide  materials  for  rebuilding  the  tissues. 

3.  They  supply  materials  that  aid  directly  or  indirectly 
in  the  general  work  of  the  body. 

117 


n8  THE   VITAL   PROCESSES 

The  Simple  Foods,  or  Nutrients.  —  From  the  great 
variety  of  things  that  are  eaten,  it  might  appear  that 
many  different  kinds  of  substances  are  suitable  for  food. 
When  our  various  animal  and  vegetable  foods  are  analyzed, 
however,  they  are  found  to  be  similar  in  composition  and 
to  contain  only  some  five  or  six  kinds  of  materials  that 
are  essentially  different.  While  certain  foods  may  contain 
only  a  single  one  of  these,  most  of  the  foods  are  mixtures 
of  two  or  more.  These  few  common  materials  which,  in 
different  proportions,  form  the  different  things  that  are 
eaten,  are  variously  referred  to  as  simple  foods,  food-stuffs, 
and  nutrients,  the  last  name  being  the  one  generally  pre- 
ferred. The  different  classes  of  nutrients  are  as  follows : 


Nutrients  • 


Proteids 

(Albuminoids) 

Carbohydrates 

Fats 

Mineral  salts 

Water 


It  is  now  necessary  to  become  somewhat  familiar  with 
the  different  nutrients  and  the  purposes  which  they  serve 
in  the  body. 

Proteids.  —  The  proteids  are  obtained  in  part  from  the 
animal  and  in  part  from  the  plant  kingdom,  there  being 
several  varieties.  A  well-known  variety,  called  albumin, 
is  found  in  the  white  of  eggs  and  in  the  plasma  of  the 
blood,  while  the  muscles  contain  an  abundance  of  another 
variety,  known  as  myosin.  Cheese  consists  largely  of  a 
kind  of  proteid,  called  casein,  which  is  also  present  in  milk, 
but  in  a  more  diluted  form.  If  a  mouthful  of  wheat  is 
chewed  for  some  time,  most  of  it  is  dissolved  and  swal- 
lowed, but  there  remains  in  the  mouth  a  sticky,  gum-like 
substance.  This  is  gluten,  a  form  of  proteid  which  occurs 


FOODS   AND   THE   THEORY    UF   DIGESTION         119 

in  different  grains.  Again,  certain  vegetables,  as  beans, 
peas,  and  peanuts,  are  rich  in  a  kind  of  proteid  which  is 
called  legnmen. 

Proteids  are  compounds  of  carbon,  hydrogen,  oxygen, 
nitrogen,  and  a  small  per  cent  of  sulphur.  Certain  ones 
(the  nucleo-proteids  from  grains)  also  contain  phosphorus. 
All  of  the  proteids  are  highly  complex  compounds  and 
form  a  most  important  class  of  nutrients. 

Purposes  of  Proteids.  —  The  chief  purpose  of  proteids 
in  the  body  is  to  rebuild  the  tissues.  Not  only  do  they 
supply  all  of  the-  main  elements  in  the  tissues,  but  they 
are  of  such  a  nature  chemically  that  they  are  readily  built 
into  the  protoplasm.  They  are  absolutely  essential  to  life, 
no  other  nutrients  being  able  to  take  their  place.  An 
animal  deprived  of  them  exhausts  the  proteids  in  its  body 
and  then  dies.  In  addition  to  rebuilding  the  tissues, 
proteids  may  also  be  oxidized  to  supply  the  body  with 
energy. 

Albuminoids  form  a  small  class  of  foods,  of  minor  importance,  which 
are  similar  to  proteids  in  composition,  but  differ  from  them  in  being 
unable  to  rebuild  the  tissues.  Gelatin,  a  constituent  of  soup  and 
obtained  from  bones  and  connective  tissue  by  boiling,  is  the  best 
known  of  the  albuminoid  foods.  On  account  of  the  nitrogen  which 
they  contain,  proteids  and  albuminoids  are  often  classed  together  as 
nitrogenous  foods, 

Carbohydrates.  —  While  the  carbohydrates  are  not  so 
essential  to  life  as  are  the  proteids,  they  are  of  very 
great  value  in  the  body.  They  are  composed  of  carbon, 
hydrogen,  and  oxygen,  and  are  obtained  mainly  from 
plants.  There  are  several  varieties  of  carbohydrates,  but 
they  are  similar  in  composition.  All  of  those  used  as 
food  to  any  great  extent  are  starch  and  certain  kinds 
of  sugar. 


120 


THE   VITAL   PROCESSES 


(Fig.  60).      From  these 


Starch  is  the  carbohydrate  of  greatest  importance  as 
a  food,  and  it  is  also  the  one  found  in  the  greatest  abun- 
dance. All  green  plants  form  more  or  less  starch,  and 
many  of  them  store  it  in  their  leaves,  seeds,  or  roots 

sources  it  is  obtained  as  food. 
Glycogen,  a  substance  closely 
resembling  starch,  is  found  in 
the  body  of  the  oyster.  It  is 
also  formed  in  the  liver  and 
muscles  of  the  higher  animals, 
being  prepared  from  the  sugar 
of  the  blood,  and  is  stored  by 
them  as  reserve  food  (Chapter 
XI).  Glycogen  is,  on  this  ac- 
count,  called  animal  starch. 

FIG.  60.  — Starch  grains  in  Starch  on  being  eaten  is  first 
cells  of  potato  as  they  appear  changed  to  sugar,  after  which  it 

may  be  converted  into  glycogen 
in  the  liver  and  in  the  muscles. 
Sugars.  —  There  are  several  varieties  of  sugar,  but  the 
important  ones  used  as  foods  fall  into  one  or  the  other 
of  two  classes,  known  as  double  sugars  (disaccharides)  and 
single  sugars  (monosaccharides).  To  the  first  class  belong 
cane  sugar,  found  in  sugar  cane  and  beets,  milk  sugar,  found 
in  sweet  milk,  and  maltose,  a  kind  of  sugar  which  is  made 
from  starch  by  the  action  of  malt.  The  important  mem- 
bers of  the  second  class  are  grape  sugar,  or  dextrose,  and 
fruit  sugar,  or  levulose,  both  of  which  are  found  in  fruits 
and  in  honey. 

The  most  important  of  all  sugars,  so  far  as  its  use  in 
the  body  is  concerned,  is  dextrose.  To  this  form  all  the 
other  sugars,  and  starch  also,  are  converted  before  they 
are  finally  used  in  the  body.  The  close  chemical  relation 


under     the     microscope 
practical  work.) 


FOODS    AND    THE    THEORY   OF   DIGESTION         12 1 

between  the  different  carbohydrates  makes  such  a  conver- 
sion easily  possible. 

Fats.  —  The  fats  used  as  foods  belong  to  one  or  the 
other  of  two  classes,  known  as  solid  fats  and  oils.  The 
solid  fats  are  derived  chiefly  from  animals,  and  the  oils 
are  obtained  mostly  from  plants.  Butter,  the  fat  of  meats, 
olive  oil,  and  the  oil  of  nuts  are  the  fats  of  greatest  im- 
portance as  foods.  Fats,  like  the  carbohydrates,  are  com- 
posed of  carbon,  hydrogen,  and  oxygen.  They  are  rather 
complex  chemical  compounds,  though  not  so  complex  as 
proteids.  Since  neither  fats  nor  carbohydrates  contain 
nitrogen,  they  are  frequently  classed  together  as  non- 
nitrogenous  foods. 

Purpose  Served  by  Carbohydrates,  Fats,  and  Albumi- 
noids.—  These  classes  of  nutrients  all  serve  the  common 
purpose  of  supplying  energy.  By  uniting  with  oxygen  at 
the  cells,  they  supply  heat  and  the  other  forms  of  bodily 
force.  This  is  perhaps  their  only  purpose.1  Proteids 
also  serve  this  purpose,  but  they  are  not  so  well  adapted 
to  supplying  energy  as  are  the  carbohydrates  and  the 
fats.  In  the  first  place  they  do  not  completely  oxidize 
and  therefore  do  not  supply  so  much  energy ;  and,  in  the 
second  place,  they  form  waste  products  that  are  removed 
with  difficulty  from  the  body. 

Mineral  Salts  and  their  Uses.  —  Mineral  salts  are 
found  in  small  quantities  in  all  of  the  more  common  food 
materials,  and,  as  a  rule,  find  their  way  into  the  body 
unnoticed.  They  supply  the  elements  which  are  found  in 
the  body  in  small  quantities  and  serve  a  variety  of  pur- 


1  While  awaiting  oxidation  at  the  cells,  the  carbohydrates  and  fats  are  stored 
up  by  the  body,  the  carbohydrates  as  glycogen  and  the  fats  as  some  form  of  fat. 
In  this  sense  they  are  sometimes  looked  upon  as  serving  to  build  up  certain  of  the 
tissues. 


122 


THE   VITAL   PROCESSES 


poses.1  Calcium  phosphate  and  calcium  carbonate  are 
important  constituents  of  the  bones  and  teeth ;  and  the 
salts  containing  iron  renew  the  hemoglobin  of  the  blood. 
Others  perform  important  functions  in  the  vital  processes. 
The  mineral  compound  of  greatest  importance  perhaps  is 
sodium  chloride,  or  common  salt.2  This  is  a  natural  con- 
stituent of  most  of  our  foods,  and  is  also  added  to  food  in 
its  preparation  for  the  table.  When  it  is  withheld  from 
animals  for  a  considerable  length  of  time,  they  suffer 
intensely  and  finally  die.  It  is  necessary  in  the  blood  and 
lymph  to  keep  their  constituents  in  solution,  and  is  thought 
to  play  an  important  rdle  in  the  chemical  changes  of  the 
cells.  It  is  constantly  leaving  the  body  as  a  waste  product 
and  must  be  constantly  supplied  in  small  quantities  in  the 
foods. 


1  The  following  table  shows  the  main  elements  in  the  body  and  their  relation 
to  the  different  nutrients  : 

f  Carbon 
I  Hydrogen 
I  Oxygen 


Elements  found 
in  the  body 


In  abundance 


Supplied  by  carbohydrates 
and  fats 


Supplied  by  proteids 


Supplied  by  different  kinds 
of  mineral  salts 


I  Nitrogen 
Sulphur 
Phosphorus 
Calcium 
In  small  quanti-Jlron 

Magnesium 
Potassium 
Sodium 
Chlorine 

2  The  recently  advanced  theory  that  the  molecules  of  the  mineral  salts,  by  dis- 
solving in  water,  separate  into  smaller  divisions,  part  of  which  are  charged  with 
positive  electricity  and  part  with  negative  electricity,  has  suggested  several  possible 
uses  for  sodium  chloride  and  other  mineral  salts  in  the  body.  The  sodium  chloride 
in  the  tissues  is  in  such  concentration  as  to  be  practically  all  separated  into  its 
sodium  and  chlorine  particles,  or  ions.  It  has  recently  been  shown  that  the  sodium 
ions  are  necessary  for  the  contraction  of  the  muscles,  including  the  muscles  of  the 
heart.  There  is  also  reason  for  believing  that  the  different  ions  may  enter  into 
temporary  combination  with  food  particles,  and  in  this  way  assist  in  the  processes 
of  nutrition. 


FOODS   AND   THE   THEORY   OF   DIGESTION         123 

Importance  of  Water.  —  Water  finds  its  way  into  the 
body  as  a  pure  liquid,  as  a  part  of  such  mixtures  as  coffee, 
chocolate,  and  milk,  and  as  a  constituent  of  all  our  solid 
foods.  (See  table  of  foods,  page  126.)  It  is  also  formed  in 
the  body  by  the  oxidation  of  hydrogen.  It  passes  through 
the  body  unchanged,  and  is  constantly  being  removed  by  all 
the  organs  of  excretion.  Though  water  does  not  liberate 
energy  in  the  body  nor  build  up  the  tissues  in  the  sense 
that  other  foods  do,  it  is  as  necessary  to  the  maintenance 
of  life  as  oxygen  or  proteids.  It  occurs  in  all  the  tissues, 
and  forms  about  70  per  cent  of  the  entire  weight  of  the 
body.  Its  presence  is  necessary  for  the  interchange  of 
materials  at  the  cells  and  for  keeping  the  tissues  soft  and 
pliable.  As  it  enters  the  body,  it  carries  digested  food 
substances  with  it,  and  as  it  leaves  it  is  loaded  with  wastes. 
Its  chief  physiological  work,  which  is  that  of  a  transporter 
of  material,  depends  upon  its  ability  to  dissolve  substances 
and  to  flow  readily  from  place  to  place. 

Relative  Quantity  of  Nutrients  Needed.  —  Proteids, 
carbohydrates,  and  fats  are  the  nutrients  that  supply  most 
of  the  body's  nourishment.  The  most  hygienic  diet  is  the 
one  which  supplies  the  proteids  in  sufficient  quantity  to 
rebuild  the  tissues  and  the  carbohydrates  and  fats  in  the 
right  amounts  to  supply  the  body  with  energy.  Much  ex- 
perimenting has  been  done  with  a  view  to  determining  these 
proportions,  but  the  results  so  far  are  not  entirely  satis- 
factory. According  to  some  of  the  older  estimates,  a  per- 
son of  average  size  requires  for  his  daily  use  five  ounces  of 
proteid,  two  and  one  half  ounces  of  fat,  and  fifteen  ounces 
of  carbohydrate.  Recent  investigations  of  this  problem 
seem  to  show  that  the  body  is  as  well,  if  not  better,  nour- 
ished by  a  much  smaller  amount  of  proteid  —  not  more 
than  two  and  one  half  ounces  (60  grams)  daily.1 

i  Chittenden,  The  Nutrition  of  Man. 


124 


THE   VITAL   PROCESSES 


While  there  is  probably  no  necessity  for  the  healthy 
individual's  taking  his  proteid,  fat,  and  carbohydrate  in 
exact  proportions  (if  the  proportions  best  suited  to  his  body 
were  known),  the  fact  needs  to  be  emphasized  that  pro- 
teids,  although  absolutely  necessary,  should  form  but  a 
small  part  (not  over  one  fifth)  of  the  daily  bill  of  fare.  In 
recognition  of  this  fact  is  involved  a  principle  of  health 
and  also  one  of  economy.  The  proteids,  especially  those 
in  meats,  are  the  most  expensive  of  the  nutrients,  whereas 
the  carbohydrates,  which  should  form  the  greater  bulk  of 
one's  food,  are  the  least  expensive. 

Effects  of  a  One-sided  Diet.  —  The  plan  of  the  body  is 
such  as  to  require  a  mixed  diet,  and  all  of  the  great  classes 
of  nutrients  are  necessary.  If  one  could  subsist  on  any 
single  class,  it  would  be  proteids,  for  proteids  are  able  both 
to  rebuild  tissue  and  to  supply  energy.  But  if  proteids 
are  eaten  much  in  excess  of  the  body's  need  for  rebuilding 
the  tissues,  and  this  excess  is  oxidized  for  supplying  energy, 
a  strain  is  thrown  upon  the  organs  of  excretion,  because 
of  the  increase  in  the  wastes.  Not  only  is  there  danger  ol 
overworking  certain  of  these  organs  (the  liver  and  kidneys), 
but  the  wastes  may  linger  too  long  in  the  body,  causing 
disorder  and  laying  the  foundation  for  disease.  On  the 
other  hand,  if  an  insufficient  amount  of  proteid  is  taken, 
the  tissues  are  improperly  nourished,  and  one  is  unable  to 
exert  his  usual  strength.  What  is  true  of  the  proteids  is 
true,  though  in  a  different  way,  of  the  other  great  classes 
of  foods.  A  diet  which  is  lacking  in  proteid,  carbohydrate, 
or  fat,  or  which  has  any  one  of  them  in  excess,  is  not 
adapted  to  the  requirements  of  the  body. 

Composition  of  the  Food  Materials.  —  One  who  intelli- 
gently provides  the  daily  bill  of  fare  must  have  some 
knowledge  of  the  nature  and  quantity  of  the  nutrients 


FOODS    AND    THE    THEORY    OF   DIGESTION 


125 


present  in  the  different  materials  used  as  food.  This  in- 
formation is  supplied  by  the  chemist,  who  has  made  exten- 
sive analyses  for  this  purpose.  Results  of  such  analyses 
are  shown  in  Table  I  (page  126),  which  gives  the  percentage 
of  proteids,  fats,  carbohydrates,  water,  and  mineral  salts 
in  the  edible  portions  of  the  more  common  of  our  foods. 

Food  Supply  to  the  Table.  —  The  main  problem  in  sup- 
plying the  daily  bill  of  fare  is  that  of  securing  through  the 


POTATO 


CHEESE  (FULL  CREAM) 


EGG 


WHITE  BREAD 


FIG.  6 1 .  —  Relative  proportions  of  different  nutrients  in  well-known  foods. 

different  food  materials  the  requisite  amounts  of  proteids, 
carbohydrates,  and  fats.  In  this  matter  a  table  showing 
the  composition  of  foods  can  be  used  to  great  advantage. 
Consulting  the  table  on  page  126,  it  is  seen  that  large  per 
cents  of  proteids  are  supplied  by  lean  meat,  eggs,  cheese, 
beans,  peas,  peanuts,  and  oatmeal,  while  fat  is  in  excess  in 
fat  meat,  butter,  and  nuts  (Fig.  61).  Carbohydrates  are 
supplied  in  abundance  by  potatoes,  rice,  corn,  sugar,  and 
molasses.  The  different  cereals  also  contain  a  large  per- 
centage of  carbohydrates  in  the  form  of  starch. 


126 


THE   VITAL   PROCESSES 


2    o  o  o  vr> 

•S        N    ON  !-•    O 
§        O    t^  M  00 


O    O  to  to  O   i-1 

vO    -  vO    -    -fr  P« 

ON  to  O    O 

M     f>  MM 


BP 

£  < 


vO  vO   to  "        OO 


00  M  OO          00  OO 

ri        ON  N 


ON       OO  OO   ^"  ONVO  vO    fO  ^^ 
rOOO    ^  ^  fO       OO  OO 


to  ON       OO  vO  CO 

ocj  tv.      oo  r^-  r^1 


vO   •-.   O   -         « 


•a      2 

C          3 
?        5 

y} 


rt  rz3 

£  e 


fa  en 


<    cq 


. 

-- 


FOODS    AND   THE   THEORY    OF   DIGESTION         127 


O   L**»  O   O   O    O 

OO    i->    M  CO  \O    f) 
flOO    M    "1  O 


"<$•  ** 

t^\cj 

i-    ro 


OO  OO  OO  CO    OCO  CO  OO  OO 


>-    t^-OO          t-^OO    H    ui 

—  -^-vd  oo  t^  6 


in  1-1   «-  \O  vO         ^  ^^   C^  <^i  N         ro  N  CO 
tsroro*^-t^inNNMOOmrON 

i_    M    «    «          »    «    w    «    t^  C^OO 


-S  § 
^  I 

> 


g-g  .   .rS 


0)      l> 

i2  -^ 

3  •* 

^  S> 

o  -° 

T3   .« 

i-.  'o* 

II 


fi 

O-  rt 


'•gi 

!/J        C 

<!    l> 
^"    o 

c    £i 


r—   ti    K 

g-  5   ° 

Ecu 


a!    4-. 


128  THE   VITAL   PROCESSES 

Variety  in  the  selection  of  foods  for  the  table  is  an  essen- 
tial feature,  but  this  should  not  increase  either  the  work  or 
the  expense  of  supplying  the  meals.  Each  single  meal 
can,  and  should,  be  simple  in  itself  and,  at  the  same  time, 
differ  sufficiently  from  the  meal  preceding  and  the  one 
following  to  give  the  necessary  variety  in  the  course  of  the 
day.  The  bill  of  fare  should,  of  course,  include  fruits  (for 
their  tonic  effects)  and  very  small  amounts  perhaps  of  sub- 
stances which  stimulate  the  appetite,  such  as  pepper,  mus- 
tard, etc.,  known  as  condiments. 

Purity  of  Food. — The  fact  that  many  of  the  food  substances  are 
perishable  makes  it  possible  for  them  to  be  eaten  in  a  slightly  decayed 
condition.  Such  substances  are  decidedly  unwholesome  (some  con- 
taining poisons)  and  should  be  promptly  rejected.  Not  only  do  fresh 
meats,  fruits,  and  vegetables  need  careful  inspection,  but  canned  and 
preserved  goods  as  well.  If  canned  foods  are  imperfectly  sealed  or  if 
not  thoroughly  cooked  in  the  canning  process,  they  decay  and  the  acids 
which  they  generate  act  on  the  metals  lining  the  cans,  forming  poison- 
ous compounds.  The  contents  of  "tin"  cans  should  for  this  reason  be 
transferred  to  other  vessels  as  soon  as  opened. 

Foods  are  also  rendered  impure  or  weakened  through  adulteration, 
the  watering  of  milk  being  a  familiar  example.  The  manufacture  of 
jellies,  preserves,  sirups,  and  various  kinds  of  pickles  and  condiments 
has  perhaps  afforded  the  largest  field  for  adulterations,  although  it  js 
possible  to  adulterate  nearly  all  of  the  leading  articles  of  food.  A  long 
step  in  the  prevention  of  food  and  drug  adulteration  was  taken  in  this 
country  by  the  passage  of  the  Pure  Food  Law.  By  forcing  manufac- 
turers of  foods  and  medicines  to  state  on  printed  labels  the  composition 
of  their  products,  this  law  has  made  it  possible  for  the  consumer  to  know 
what  he  is  purchasing  and  putting  into  his  body. 

Alcohol  not  a  Food.  —  Many  people  in  ,this  and  other 
countries  drink  in  different  beverages,  such  as  whisky, 
beer,  wine,  etc.,  a  varying  amount  of  alcohol.  This  sub- 
stance has  a  temporary  stimulating  or  exciting  effect,  and 
the  claim  has  been  made  that  it  serves  as  a  food.  Recently 


FOODS   AND    THE   THEORY   OF   DIGESTION         129 

it  has  been  shown  that  alcohol  when  introduced  into  the 
body  in  small  quantities  and  in  a  greatly  diluted  form,  is 
nearly  all  oxidized,  yielding  energy  as  does  fat  or  sugar. 
If  no  harmful  effects  attended  the  use  of  alcohol,  it  might 
on  this  account  be  classed  as  a  food.  But  alcohol  is  known 
to  be  harmful  to  the  body.  When  used  in  large  quantities, 
it  injures  nearly  all  of  the  tissues,  and  when  taken  habit- 
ually, even  in  small  doses,  it  leads  to  the  formation  of  the 
alcohol,  habit  which  is  now  recognized  and  treated  as  a 
disease.  This  and  other  facts  show  that  alcohol  is  not 
adapted  to  the  body  plan  of  taking  on  and  using  new 
material  (Chapter  XI),  and  no  substance  lacking  in  this  re- 
spect can  properly  be  classed  as  a  food.1  Instead  of  class- 
ing alcohol  as  a  food,  it  should  be  placed  in  that  long  list 
of  substances  which  are  introduced  into  the  body  for  spe- 
cial purposes  and  which  are  known  by  the  general  name  of 
Drugs.  —  Drugs  act  strongly  upon  the  body  and  tend  to 
bring  about  unusual  and  unnatural  results.  Their  use 
should  in  noway  be  confused  with  that  of  foods.  If  taken 
in  health,  they  tend  to  disturb  the  physiological  balance  of 
the  body  by  unduly  increasing  or  diminishing  the  action 
of  the  different  organs.  In  disease  where  this  balance  is 
already  disturbed,  they  may  be  administered  for  their  coun- 
teractive effects,  but  always  under  the  advice  and  direction 
of  a  physician.  Knowing  the  nature  of  the  disturbance 
which  the  drug  produces,  the  physician  can  administer  it 
to  advantage,  should  the  body  be  out  of  physiological 

1  While  alcohol  cannot  be  classed  as  a  food,  it  is  believed  by  some  authorities 
to  contain  food  value  and,  in  the  hands  of  the  physician,  to  be  a  substance  capable 
of  rendering  an  actual  service  in  the  treatment  of  certain  diseases.  It  might,  for 
example,  be  used  where  one's  power  of  digestion  is  greatly  impaired,  since  alcohol 
requires  no  digestion.  But  upon  this  point  there  is  a  decided  difference  of  opinion. 
Certain  it  is  that  no  one  should  attempt  to  use  alcohol  as  food  or  medicine  except 
under  the  advice  and  direction  of  his  physician. 


I30  THE   VITAL   PROCESSES 

balance,  or  diseased.     Not  only  are  drugs  of  no  value  in 
health,  but  their  use  is  liable  to  do  much  harm. 

NATURE  OF  DIGESTION 

Before  the  nutrients  can  be  oxidized  at  the  cells,  or  built 
into  the  protoplasm,  they  undergo  a  number  of  changes. 
These  are  necessary  for  their  entrance  into  the  body,  for 
their  distribution  by  the  blood  and  the  lymph,  and  for  the 
purposes  which  they  finally  serve.  The  first  of  these 
changes  is  preparatory  to  the  entrance  of  the  nutrients  and 
is  known  as  digestion.  The  organs  which  bring  about 
this  change,  called  digestive  organs,  have  a  special  con- 
struction which  adapts  them  to  their  work.  It  will  assist 
materially  in  understanding  these  organs  if  we  first  learn 
something  of  the  nature  of  the  work  which  they  have  to 
perform. 

How  the  Nutrients  get  into  the  Body.  —  The  nature  of 
digestion  is  determined  by  the  conditions  affecting  the 
entrance  of  nutrients  into  the  body.  Food  in  the  stomach 
and  air  in  the  lungs,  although  surrounded  by  the  body,  are 
still  outside  of  what  is  called  the  body  proper.  To  gain 
entrance  into  the  body  proper,  a  substance  must  pass 
through  the  body  wall.  This  consists  of  the  skin  on  the 
outside  and  of  the  mucous  linings  of  the  air  passages  and 
other  tubes  and  cavities  which  are  connected  with  the 
external  surface. 

To  get  from  the  digestive  organs  into  the  blood,  the 
nutrients  must  pass  through  the  mucous  membrane  lining 
these  organs  and  also  the  walls  of  blood  or  lymph  vessels. 
Only  liquid  materials  can  make  this  passage.  It  is  neces- 
sary, therefore,  to  reduce  to  the  liquid  state  all  nutrients 
not  already  in  that  condition.  This  reduction  to  the  liquid 
state  constitutes  the  digestive  process. 


FOODS   AND   THE   THEORY   OF   DIGESTION         131 

How  Substances  are  Liquefied.  —  While  the  reduction  of 
solids  to  the  liquid  state  is  accomplished  in  some  instances 
by  heating  them  until  they  melt,  they  are  more  frequently 
reduced  to  this  state  by  subjecting  them  to  the  action  of 
certain  liquids,  called  solvents.  Through  the  action  of  the 
solvent  the  minute  particles  of  the  solid  separate  from 
each  other  and  disappear  from  view.  (Shown  in  dropping 
salt  in  water.)  At  the  same  time  they  mix  with  the  solvent, 
forming  a  solution,  from  which  they  separate  -only  with 
great  difficulty.  For  this  reason  solids  in  solution  can  dif- 
fuse through  porous  partitions  along  with  the  solvents  in 
which  they  are  dissolved  (page  73). 

By  digestion  the  nutrients  are  reduced  to  the  form  of  a 
solution.  The  process  is,  simply  speaking,  one  of  dissolv- 
ing. The  liquid  employed  as  the  digestive  solvent  is  water. 
The  different  nutrients  dissolve  in  water,  mixing  with  it 
to  form  a  solution  which  is  then  passed  into  the  body 
proper. 

Digestion  not  a  Simple  Process.  —  Digestion  is  by  no 
means  a  simple  process,  such,  for  instance,  as  the  dissolv- 
ing of  salt  or  sugar  in  water.  These,  being  soluble  in 
water,  dissolve  at  once  on  being  mixed  with  a  sufficient 
amount  of  this  liquid.  The  majority  of  the  nutrients,  how- 
ever, are  insoluble  in  water  and  are  unaffected  by  it  when 
acting  alone.  Fats,  starch,  and  most  of  the  proteids  do 
not  dissolve  in  water.  Before  these  can  be  dissolved  they 
have  to  be  changed  chemically  and  converted  into  sub- 
stances that  are  soluble  in  water.  This  complicates  the 
process  and  prevents  the  use  of  water  alone  as  the  digestive 
solvent. 

A  Similar  Case.  —  If  a  piece  of  limestone  be  placed  in 
water,  it  does  not  dissolve,  because  it  is  insoluble  in  water. 
If  hydrochloric  acid  is  now  added  to  the  water,  the  lime- 


I32  THE   VITAL   PROCESSES 

stone  is  soon  dissolved  (Fig.  62).    (See  Practical  Work.)   It 
seems  at  first  thought  that  the  acid  dissolves  the  limestone, 
but  this  is  not  the  case.      The  acid  pro- 
duces a  chemical  change  in  the  limestone 
(calcium  carbonate)  and  converts  it  into  a 
compound  (calcium  chloride)  that  is  soluble 
in  water.     As  fast  as  this  is  formed  it  is 
dissolved  by  the  water,  which  is  the  real 
solvent  in  the  case.    The  acid  simply  plays 
FIG.  62.  — The    the  part  of  a  chemical  converter, 
dissolving  of  lime-        Thg  Digestive  Fluids.  —  Several  fluids  — 

stone  in  water  con-  .      .    .         ... 

taining  acid,  sug-  sah.va,  gastnc  ]ulce>  pancreatic  juice,  bile, 
gesting  the  double  and  intestinal  juice  —  are  employed  in  the 
action  in  the  di-  digestion  of  the  food.  The  composition  of 

gestion  of  most  these  fluMs  jg  jn  k  ing  with  the  nature 
foods. 

of  the  digestive  process.  While  all  of  them 
have  water  for  their  most  abundant  constituent,  there  are 
dissolved  in  the  water  small  amounts  of  active  chemical 
agents.  It  is  the  work  of  these  agents  to  convert  the 
insoluble  nutrients  into  substances  that  are  soluble  in 
water.  The  digestive  fluids  are  thus  able  to  act  in  a  double 
manner  on  the  nutrients  —  to  change  them  chemically  and 
to  dissolve  them.  The  chemical  agents  which  bring 
about  the  changes  in  the  nutrients  are  called  enzymes,  or 
digestive  ferments. 

Foods  Classed  with  Reference  to  Digestive  Changes.  — 
With  reference  to  the  changes  which  they  undergo  during 
digestion,  foods  may  be  divided  into  three  classes  as  follows: 

1.  Substances  already  in  the  liquid  state  and  requiring 
no  digestive  action.     Water  and  solutions  of  simple  foods 
in  water  belong  to  this  class.     Milk  and  liquid  fats,  or  oils, 
do  not  belong  to  this  class. 

2.  Solid  foods  soluble  in  water.      This  class  includes 


FOODS    AND   THE   THEORY   OF    DIGESTION         133 

common  salt  and  sugar.  These  require  no  digestive  action 
other  than  dissolving  in  water. 

3.  Foods  that  are  insoluble  in  water.  These  have  first 
to  be  changed  into  soluble  substances,  after  which  they 
are  dissolved. 

Summary.  —  Materials  called  foods  are  introduced  into 
the  body  for  rebuilding  the  tissues,  supplying  energy,  and 
aiding  in  its  general  work.  Only  a  few  classes  of  sub- 
stances, viz.,  proteids,  carbohydrates,  fats,  water,  and  some 
mineral  compounds  have  all  the  qualities  of  foods  and  are 
suitable  for  introduction  into  the  body.  Substances  known 
as  drugs,  which  may  be  used  as  medicines  in  disease, 
should  be  avoided  in  health.  Before  foods  can  be  passed 
into  the  body  proper,  they  must  be  converted  into  the 
liquid  form,  or  dissolved.  In  this  process,  known  as  diges- 
tion, water  is  the  solvent ;  and  certain  chemical  agents, 
called  enzymes,  convert  the  insoluble  nutrients  into  sub- 
stances that  are  soluble  in  water. 

Exercises.  —  i .  How  does  oxidation  at  the  cells  make  necessary  the 
introduction  of  new  materials  into  the  body  ?  ^ 

2.  What  different  purposes  are  served  by  the  foods  ? 

3.  What  is  a  nutrient  ?     Name  the  important  classes. 

4.  What  are  food  materials  ?    From  what  sources  are  they  obtained  ? 

5.  Name  the  different  kinds  of  proteids;  the  different  kinds  of  car- 
bohydrates.    Why  are  proteids  called  nitrogenous  foods  and  fats  and 
carbohydrates  non-nitrogenous  foods  ? 

6.  Show  why  life  cannot  be  carried  on  without  proteids ;   without 
water. 

7.  What  per  cents  of  proteid,  fat,  and  carbohydrate  are  found  in 
wheat  flour,  oatmeal,  rice,  butter,  potatoes,  round  beef,  eggs,  and  pea- 
nuts ? 

8.  State  the  objection  to  a  meal  consisting  of  beef,  eggs,  beans, 
bread,  and  butter;  to  one  consisting  of  potatoes,  rice,  bread,  and  butter. 
Which  is  the  more  objectionable  of  these  meals  and  why  ? 

9.  State  the  general  plan  of  digestion. 


,34  THE   VITAL   PROCESSES 

10.    Show  that  digestion  is  not  a  simple  process  like  that  of  dissolv- 
ing salt  in  water. 


Elements  supplied  by  the  Foods.— The  following  brief  study  will 
enable  the  pupil  to  identify  most  of  the  elements  present  in  the  body 
and  which  have,  therefore,  to  be  supplied  by  the  foods. 

Carbon.  —  Examine  pieces  of  charred  wood,  coke,  or  coal,  and  also 
the  "  lead  "  in  lead  pencils.  Show  that  the  charred  wood  and  the  coal 
will  burn.  Recall  experiment  (page  114)  showing  that  carbon  in  burn- 
ing forms  carbon  dioxide. 

Hydrogen.  —  Fill  a  test  tube  one  third  full  of  strong  hydrochloric 
acid  and  drop  into  it  several  small  scraps  of  zinc.  The  gas  which  is 
evolved  is  hydrogen.  When  the  hydrogen  is  coming  off  rapidly,  bring 
a  lighted  splinter  to  the  mouth  of  the  tube.  The  gas  should  burn. 
Hold  a  cold  piece  of  glass  over  the  flame  and  observe  the  deposit  of 
moisture.  Hydrogen  in  burning  forms  water.  Extinguish  the  flame 
by  c&vering  the  top  of  the  tube  with  a  piece  of  cardboard.  Now  let  the 
escaping  gas  collect  in  a  tumbler  inverted  over  the  tube.  After  hold- 
ing the  tumbler  in  this  position  for  two  or  three  minutes,  remove  and, 
keeping  inverted,  thrust  a  lighted  splinter  into  it.  (The  gas  should 
either  burn  or  explode.)  What  does  this  experiment  show  relative  to 
the  weight  of  hydrogen  as  compared  with  that  of  air? 

Nitrogen.  —  Nitrogen  forms  about  four  fifths  of  the  atmosphere, 
where,  like  oxygen,  it  exists  in  a  free  state.  It  may  be  separated  from 
the  oxygen  of  an  inclosed  portion  of  air  by  causing  that  gas  to  unite 
with  phosphorus.  Place  a  piece  of  phosphorus  the  size  of  a  pea  in  a 
depression  in  a  flat  piece  of  cork.  (Handle  phosphorus  with  wet  fingers 
or  with  forceps.)  Place  the  cork  on  water  and  have  ready  a  glass  fruit 
jar  holding  not  more  than  a  quart.  Ignite  the  phosphorus  with  a  hot 
wire  and  invert  the  jar  over  it,  pushing  the  mouth  below  the  surface  of 
the  water.  The  phosphorus  uniting  with  the  oxygen  fills  the  jar  with 
white  fumes  of  phosphoric  oxide.  These  soon  dissolve  in  the  water, 
leaving  a  clear  gas  above.  This  is  nitrogen.  Place  a  cardboard  under 
the  mouth  of  the  jar  and  turn  it  right  side  up,  leaving  in  the  water  and 
keeping  the  top  covered.  Light  a  splinter  and,  slipping  the  cover  to 
one  side,  thrust  the  flame  into  the  jar  of  nitrogen,  noting  the  effect. 
(Flame  is  extinguished.)  Compare  nitrogen  with  oxygen  in  its  relation 
to  combustion.  What  purpose  is  served  by  each  in  the  atmosphere? 


FOODS    AND    THE   THEORY    OF    DIGESTION         135 

O.iygert.  —  Review  experiments  (page  114)  showing  the  properties 
of  oxygen. 

Phosphorus.  —  Examine  a  small  piece  of  phosphorus,  noting  that  it 
has  to  be  kept  under  water.  Lay  a  small  piece  on  the  table  and  observe 
the  tiny  stream  of  white  smoke  rising  from  it,  formed  by  slow  oxida- 
tion. Dissolve  a  piece  as  large  as  a  pea  in  a  teaspoonful  of  carbon 
disulphide  in  a  test  tube,  pour  this  on  a  piece  of  porous  paper,  and  lay 
the  paper  on  an  iron  support.  When  the  carbon  disulphide  evaporates 
the  phosphorus  takes  fire  spontaneously.  (The  heat  from  the  slow 
oxidation  is  sufficient  to  ignite  the  phosphorus  in  the  finely  divided 
condition.)  What  is  the  most  striking  property  of  phosphorus?  What 
purpose  does  it  serve  in  the  match  ? 

Sulphur.  —  Examine  some  sulphur,  noting  its  color  and  the  absence 
of  odor  or  taste.  (Impure  sulphur  may  have  an  odor  and  a  taste.) 
Burn  a  little  sulphur  in  an  iron  spoon,  noting  that  the  compound  which 
it  forms  with  oxygen  by  burning  has  a  decided  odor. 

Other  Elements.  —  Magnesium.  Examine  and  burn  a  piece  of 
magnesium  ribbon,  noting  the  white  compound  of  magnesium  oxide 
which  is  formed.  Iron.  Examine  pieces  of  the  metal  and  also  some 
of  its  compounds,  as  ferrous  sulphate,  ferric  chloride,  and  ferric  oxide 
or  iron  rust.  Sodium.  Drop  a  piece  of  the  metal  on  water  and  observe 
results.  Sodium  decomposes  water.  It  has  to  be  kept  under  some 
liquid,  such  as  kerosene,  which  contains  no  oxygen.  (It  should  not  be 
touched  except  with  the  fingers  wet  with  kerosene.)  Chlorine.  Pour 
strong  hydrochloric  acid  on  a  little  manganese  dioxide  in  a  test  tube, 
and  warm  gently  over  a  low  flame.  The  escaping  gas  is  chlorine. 
Avoid  breathing  much  of  it. 

Composition  of  the  Nutrients. — The  simplest  way  of  determining 
what  elements  make  up  the  different  nutrients  is  by  heating  them  and 
studying  the  products  of  decomposition,  as  follows  : 

To  show  that  Carbohydrates  contain  Carbon,  Hydrogen,  and  Oxy- 
gen. —  Place  one  half  teaspoonful  of  powdered  starch  in  a  test  tube  and 
heat  strongly.  Observe  that  water  condenses  on  the  sides  of  the  tube 
and  that  a  black,  charred  mass  remains  behind.  The  black  mass  consists 
mainly  of  carbon.  The  water  is  composed  of  hydrogen  and  oxygen. 
These  three  elements  are  thus  shown  to  be  present  in  the  starch.  The 
experiment  may  be  repeated,  using  sugar  instead  of  starch. 

To  show  that  Proteids  contain  Carbon,  Hydrogen,  Oxygen,  Nitrogen, 
and  Sulphur.  —  Place  in  a  test  tube  some  finely  divided  proteid 


I36  THE   VITAL   PROCESSES 

which  has  been  thoroughly  dried  (dried  beef  .or  the  lean  of  hard  cured 
bacon).  Heat  strongly  in  the  hood  of  a  chemical  laboratory  or  some 
other  place  where  the  odors  do  not  get  into  the  room.  First  hold  in 
the  escaping  gases  a  wet  strip  of  red  litmus  paper.  This  will  be  turned 
blue,  showing  ammonia  (NH3)  to  be  escaping.  Next  hold  in  the 
mouth  of  the  tube  a  strip  of  a  paper  wet  with  a  solution  of  lead  nitrate. 
This  is  turned  black  or  brown  on  account  of  hydrogen  sulphide  (H2S) 
which  is  being  driven  off.  Observe  also  that  water  condenses  in  the 
upper  part  of  the  tube  and  that  a  black,  charred  mass  remains  behind. 
Since  the  products  of  decomposition  (H,O,  NH3,  H^S,  and  the  charred 
mass)  contain  hydrogen,  oxygen,  nitrogen,  sulphur,  and  carbon,  these 
elements  are  of  course  present  in  the  proteid  tested. 

To  show  the  Presence  of  Mineral  Matter.  —  Burn  a  piece  of  dry 
bread  by  holding  it  in  a  clear,  hot  flame,  and  observe  the  ash  that  is 
left  behind.  This  is  the  mineral  matter  present  in  the  bread. 

Tests  for  Nutrients.  Proteids.  —  Cover  the  substance  to  be  tested 
with  strong, nitric  acid  and  heat  gradually  to  boiling.  If  proteid  is  pres- 
ent it  turns  yellow  and  partly  dissolves  in  the  acid,  forming  a  yellow 
solution.  Let  cool  and  then  add  ammonia.  The  yellow  solid  and  the 
solution  are  turned  a  deep  orange  color.  Apply  this  test  to  foods  con- 
taining proteid  such  as  white  of  egg,  cheese,  lean  meat,  etc. 

Starch.  —  (a)  Place  a  small  lump  of  starch  in  one  fourth  of  a  pint  of 
water  and  heat  gradually  to  boiling,  stirring  well.  Then  add  enough 
water  to  form  a  thin  liquid  and  fill  a  test  tube  half  full.  Add  to  this 
a  few  drops  of  a  solution  of  iodine.  (Prepare  by  dissolving  a  crystal 
of  iodine  in  25  cubic  centimeters  (^  pint)  of  a  solution  of  potassium 
iodide  in  water  and  add  water  to  this  until  it  is  a  light  amber  color.) 
The  starch  solution  is  turned  blue,  (b)  Cut  with  a  razor  a  thin  slice 
from  a  potato.  Place  this  in  a  weak  solution  of  iodine  for  a  few 
minutes'  and  then  examine  with  the  microscope,  using  first  a  low  and 
then  a  high  power.  Numerous  starch  grains  inclosed  in  cellulose  walls 
will  be  seen  (Fig.  60). 

Dextrose,  or  Grape  Sugar.  —  Place  a  solution  of  the  substance  sup- 
posed to  contain  grape  sugar  in  a  test  tube  and  add  a  few  drops  of  a 
dilute  solution  of  copper  sulphate.  Then  add  sodium  hydroxide  solu- 
tion until  the  precipitate  which  first  forms  is  redissolved  and  a  clear  blue 
liquid  obtained.  Heat  the  upper  portion  of  the  liquid  slowly  to  near 
the  boiling  point.  A  little  below  the  boiling  point  the  blue  color  dis- 
appears and  a  yellow-red  precipitate  is  formed.  If  the  upper  layer  of 


FOODS    AND   THE   THEORY    OF    DIGESTION         137 

the  liquid  is  now  boiled,  the  color  deepens  and  this  may  be  contrasted 
with  the  blue  color  below.  Apply  this  test  to  the  sugar  in  raisins  and 
in  honey. 

Fat.  —  Fat  is  recognized  by  its  effect  on  paper,  making  a  greasy  stain 
which  does  not  disappear  on  heating  and  which  renders  the  paper  trans- 
lucent. Try  butter,  lard,  or  olive  oil.  Also  show  the  presence  of  fat  in 
peanuts  by  crushing  them  in  a  mortar  and  rubbing  the  powder  on  thin 
paper.  If  the  substance  to  be  tested  contains  but  little  fat,  this  may  be 
dissolved  out  with  ether.  If  a  drop  of  ether  containing  the  fat  is  placed 
on  paper,  it  evaporates,  leaving  the  fat,  which  then  forms  the  stain. 

To  show  the  Effect  of  Alcohol  upon  Proteid.  —  Place  some  of  the 
white  of  a  raw  egg  in  a  glass  vessel  and  cover  it  with  a  small  amount  of 
alcohol.  As  the  albumin  (proteid)  hardens,  or  coagulates,  observe  that 
the  quantity  of  clear  liquid  increases.  This  is  due  to  the  withdrawal 
of  water  from  the  albumin  by  the  alcohol.  Since  the  tissues  are  made 
up  chiefly  of  proteids,  a  piece  of  muscle  or  of  liver  may  be  used  in  the 
experiment,  instead  of  the  egg,  with  similar  results. 

To  illustrate  the  Digestive  Process.  —  To  a  tumbler  two  thirds  full 
of  water  add  a  little  salt.  Stir  and  observe  that  the  salt  is  dissolved. 
Taste  the  solution  to  see  that  the  salt  has  not  been  changed  chemically. 
Now  add  a  little  powdered  limestone  to  the  water  and  stir  as  before. 
Observe  that  the  limestone  does  not  dissolve.  Then  add  some  hydro- 
chloric acid  and  observe  the  result.  State  the  part  played  by  the  acid 
and  by  the  water  in  dissolving  the  limestone.  Apply  to  the  digestion 
of  the  different  classes  of  foods. 


CHAPTER   X 
ORGANS  AND  PROCESSES  OF  DIGESTION 

THE  organs  of  digestion  are  adapted  to  the  work  of  dis 
solving  the  foods  by  both  their  structure  and  arrangement. 
Most  of  them  consist  either  of  tubes  or  cavities  and  these 
are  so  connected,  one  with  the  other,  as  to  form  a  contin- 
uous passageway  entirely  through  the  body.  This  pas- 
sageway is  known  as 

The  Alimentary  Canal. — The  alimentary  canal  has  a 
length  of  about  thirty  feet  and,  while  it  begins  at  the 
mouth,  all  but  about  eighteen  inches  of  it  is  found  in  the 
abdominal  cavity.  On  account  of  its  length  it  lies  for 
the  most  part  in  coils,  the  two  largest  ones  being  known 
as  the  small  irltestine  and  the  large  intestine.  Connected 
with  the  alimentary  canal  are  the  glands  that  supply  the 
liquids  for  acting  on  the  food.  The  divisions  of  the  canal 
and  most  of  the  glands  that  empty  liquids  into  it  are  shown 
in  Fig.  63  and  named  in  the  table  below: 


f              .  1 

Mouth,  containing  teeth  and 

tongue 

Pharynx       f             f  Duodenum 

Parts  of 

Esophagus 

Small  j  Jejunum 

Alimentary 

Stomach 

[  Ileum 

Canal 

Intestines    • 

f  Caecum  and  vermiform 

appendix 

Ascending 

Digestive 
Organs    • 

.  Large 

Colon  •< 

Transverse 
Descending 
Sigmoid  flex- 

ure 

Rectum 

f  Parotid 

Digestive 

Salivary  j  Submaxillary 
Gastric    (  Sublingual 

X 

Glands 

Liver 

* 

Pancreas 

>>  Intestinal 

138 


ORGANS    AND    PROCESSES    OF   DIGESTION 


139 


Coats  of  the  Alimentary  Canal.  — 
The  walls  of  the  alimentary  canal, 
except  at  the  mouth,  are  distinct 
from  the  surrounding  tissues  and 
consist  in  most  places  of  at  least 
three  layers,  or  coats,  as  follows : 

1.  An  inner  coat,  or  lining,  known 
as    the    mucous   membrane.      This 
membrane   is   not   confined    to   the 
alimentary  canal,   but   lines,  as  we 
have  seen,  the  different  air  passages. 
It  covers,  in  fact,  all  those  internal 
surfaces  of  the  body  that    connect 
with  the  external  surface.    It  derives 
its  name  from  the  substance  which 
it  secretes,  called  mucus.     In  struc- 
ture   it    resembles   the    skin,  being 
continuous  with  the  skin  where  cavi- 
ties open  to  the  surface.     It  is  made 
up  of   two  layers  —  a  thick  under- 
layer  which  contains  blood  vessels, 
nerves,  and  glands,  and  a  thin  sur- 
face   layer,    called    the    epithelium. 
The  epithelium,  like  the  cuticle,  is 
without    blood   vessels,    nerves,    or 
glands. 

2.  A  middle  coat,  which  is  mus- 
cular and  which  forms  a  continuous 
layer  throughout  the  canal,  except 
at  the  mouth.      (Here  its  place  is 
taken    by    the    strong     muscles    of 
mastication  which  are  separate  and 
distinct   from    each    other.)      As   a 


10 


FIG.  63.  —  Diagram  of 
the  digestive  system. 
I.  Mouth.  2.  Soft  palate. 
3.  Pharynx.  4.  Parotid  gland. 
5.  Sublingual  gland.  6.  Sub- 
maxillary  gland.  7.  Esoph- 
agus. 8.  Stomach.  9.  Pan- 
creas. 10.  Vermiform  ap- 
pendix, n.  Caecum.  12. 
Ascending  colon.  13.  Trans- 
verse colon.  14.  Descend- 
ing colon.  15.  Sigmoid  flex- 
ure. 1 6.  Rectum.  17.  Ileo- 
csecal  valve.  18.  Duct  from 
liver  and  pancreas.  1 9.  Liver. 

Diagram  does  not  show 
comparative  length  of  the 
small  intestine. 


140 


THE    VITAL   PROCESSES 


rule  the  muscles  of  this  coat  are  involuntary.  They  sur- 
round the  canal  as  thin  sheets  and  at  most  places  form 
two  distinct  layers.  In  the  inner  layer  the  fibers  encircle 
the  canal,  but  in  the  outer  layer  they  run  longitudinally, 
or  lengthwise,  along  the  canal.1 

3.  An  outer  or  serous  coat,  which  is  limited  to  those  por- 
tions of  the  canal  that  occupy  the  abdominal  cavity.  This 

coat  is  not  found  above  the  dia- 
phragm. It  is  a  part  of  the 
lining  membrane  of  the  cavity  of 
the  abdomen,  called 

The  Peritoneum.  —  The  peri- 
toneum is  to  the  abdominal  cavity 
what  the  pleura  is  to  the  thoracic 
cavity.  It  forms  the  outer  cover- 
ing for  the  alimentary  canal  and 
other  abdominal  organs  and  sup- 
plies the  inner  lining  of  the  cav- 
ity itself.  It  is  also  the  means 
of  holding  these  organs  in  place, 
some  of  them  being  suspended 
by  it  from  the  abdominal  walls 

(Fig.  64).     By  the  secretion  of 
FIG.  64.  — Diagram  of  the 
peritoneum.          i.    Transverse     a  sma11  amount   of   liquid,  it  pre- 

colon.   2.  Duodenum.   3.  Small    vents  friction  of  the  parts  upon 

intestine.     4.  Pancreas.  one  another. 

Digestive  Glands.  —  The  glands  which  provide  the  dif- 
ferent fluids  for  acting  on -the  foods  derive  their  constitu- 
ents from  the  blood.  They  are  situated  either  in  the 
mucous  membrane  or  at  convenient  places  outside  of  the 


1  A  layer  of  connective  tissue  between  the  mucous  membrane  and  the  muscular 
coat  is  usually  referred  to  as  the  submucovs  coat.  This  contains  numerous  blood 
vessels  and  nerves  and  binds  the  muscular  coat  to  the  mucous  membrane. 


ORGANS    AND    PROCESSES    OF    DIGESTION         141 

canal  and  pass  their  liquids  into  it  by  means  of  small  tubes, 
called  ducts.  In  the  canal  the  food  and  the  digestive 
fluids  come  in  direct  contact  —  a  condition  which  the  dis- 
solving processes  require.  Each  kind  of  fluid  is  secreted 
by  a  special  kind  of  gland  and  is  emptied  into  the  canal 
at  the  place  where  it  is  needed. 

The  Digestive  Processes. — Digestion  is  accomplished  by 
acting  upon  the  food  in  different  ways,  as  it  is  passed  along 
the  canal,  with  the  final  result  of  reducing  it  to  the  form 
of  a  solution.  Several  distinct  processes  are  necessary 
and  they  occur  in  such  an  order  that  those  preceding  are 
preparatory  to  those  that  follow.  These  processes  are 
known  as  mastication,  insalivation,  deglutition,  stomach 
digestion,  and  intestinal  digestion.  As  the  different  mate- 
rials become  liquefied  they  are  transferred  to  the  blood, 
and  substances  not  reduced  to  the  liquid  state  are  passed 
on  through  the  canal  as  waste.  The  first  two  of  the  di- 
gestive processes  occur  in 

The  Mouth. — This  is  an  oval-shaped  cavity  situated  at 
the  very  beginning  of  the  canal.  It  is  surrounded  by  the 
lips  in  front,  by  the  cheeks  on  the  sides,  by  the  hard 
palate  above  and  the  soft  palate  behind,  and  by  the  tissues 
of  the  lower  jaw  below.  The  mucous  membrane  lining 
the  mouth  is  soft  and  smooth,  being  covered  with  flat 
epithelial  cells.  The  external  opening  of  the  mouth  is 
guarded  by  the  lips,  and  the  soft  palate  forms  a  movable 
partition  between  the  mouth  and  the  pharynx.  In  a  con- 
dition of  repose  the  mouth  space  is  practically  filled  by  the 
teeth  and  the  tongue,  but  the  cavity  may  be  enlarged  and 
room  provided  for  food  by  depressing  the  lower  jaw. 

The  mouth  by  its  construction  is  well  adapted  to  carry- 
ing on  the  processes  of  mastication  and  insalivation.  By 
the  first  process  the  solid  food  is  reduced,  by  the  cutting 


142 


THE   VITAL   PROCESSES 


and  grinding  action  of  the  teeth,  to  a  finely  divided  condi- 
tion. By  the  second,  the  saliva  becomes  mixed  with  the 
food  and  is  made  to  act  upon  it. 

Accessory  Organs  of  the  Mouth. — The  work  of  mastica- 
tion and  insalivation  is  accomplished  through  organs  situ- 
ated in  and  around  the  mouth  cavity.  These  comprise : 

i.  The  Teeth.  —  The  teeth  are  set  in  the  upper  and 
lower  jaws,  one  row  directly  over  the  other,  with  their 

hardened  sur- 
faces facing.  In 
reducing  the  food, 
the  teeth  of  the 
lower  jaw  move 
against  those  of 
the  upper,  while 
the  food  is  held 
by  the  tongue  and 
cheeks  between 
the  grinding  sur- 
faces. The  front 
teeth  are  thin  and 
FIG.  65.  —  The  teeth.  A.  Section  of  a  single  chisel-shaped, 
molar,  i.  Pulp.  2.  Dentine.  3.  Enamel.  4.  Crown.  They  do  not  meet 
5.  Neck.  6.  Root.  B.  Teeth  in  position  in  lower  jaw. 

1.  Incisors.     2.  Canine.     3.  Biscuspids.     4.  Molars.    so  squarely  as  do 

C.  Upper  and  lower  teeth  on  one  side.     I.  Incisors,    the  back  ones,  but 

2.  Canines.     3.  Bicuspids.     4.  Molars.     5.  Wisdom,    their    edges    glide 

D.  Upper  and  lower  incisor,  to  show  gliding  contact.  , , 

over  each  other, 

like  the  blades  of  scissors  —  a  condition  that  adapts  them 
to  cutting  off  and  separating  the  food  (D,  Fig.  65).  The 
back  teeth  are  broad  and  irregular,  having  surfaces  that 
are  adapted  to  crushing  and  grinding. 

Each  tooth  is   composed  mainly  of  a  bone-like  substance,  called 
dentine,  which  surrounds  a  central  space,  containing  blood  vessels  and 


D 


ORGANS    AND    PROCESSES    OF   DIGESTION         143 

nerves,  known  as  the  pulp  cavity.  It  is  set  in  a  depression  in  the  jaw 
where  it  is  held  firmly  in  place  by  a  bony  substance,  known  as  cement. 
The  part  of  the  tooth  exposed  above  the  gum  is  the  crown,  the  part 
surrounded  by  the  gum  is  the  neck,  and  the  part  which  penetrates  into 
the  jaw  is  the  root  (A,  Fig.  65).  A  hard,  protective  material,  called 
enamel,  covers  the  exposed  surface  of  the  tooth. 

The  teeth  which  first  appear  are  known  as  the  temporary,  or  milk, 
teeth  and  are  twenty  in  number,  ten  in  each  jaw.  They  usually  begin 
to  appear  about  the  sixth  month,  and  they  disappear  from  the  mouth 
at  intervals  from  the  sixth  to  the  thirteenth  year.  As  they  leave,  teeth 
of  the  second,  or  permanent,  set  take  their  place.  This  set  has  thirty- 
two  teeth  of  four  different  kinds  arranged  in  the  two  jaws  as  follows  : 

In  front,  above  and  below,  are  four  chisel-shaped  teeth,  known  as 
the  incisors.  Next  to  these  on  either  side  is  a  tooth  longer  and  thicker 
than  the  incisors,  called  the  canine.  Back  of  these  are  two  short, 
rounded  and  double  pointed  teeth,  the  bicuspids,  and  back  of  the  bicus- 
pids are  three  heavy  teeth  with  irregular  grinding  surfaces,  called  the 
molars  (B  and  C,  Fig.  65).  Since  the  molar  farthest  back  in  each  jaw 
is  usually  not  cut  until  maturity,  it  is  called  a  wisdom  tooth.  The  molars 
are  known  as  the  superadded 
permanent  teeth  because  they 
do  not  take  the  place  of  milk 
teeth,  but  form  farther  back 
as  the  jaw  grows  in  length. 


2 .   The  Tongue.  —  The 
tongue  is  a  muscular  or- 
gan whose  fibers  extend     FlG-  66.  — Diagram  showing  directions 
,       .^      .  of  muscular  fibers  in  tongue. 

through    it    in    several 

directions  (Fig.  66).  Its  structure  adapts  it  to  a  variety  of 
movements.  During  mastication  the  tongue  transfers  the 
food  from  one  part  of  the  mouth  to  another,  and,  with 
the  aid  of  the  cheeks,  holds  the  food  between  the  rows 
of  teeth.  (By  an  outward  pressure  from  the  tongue  and 
an  inward  pressure  from  the  cheek  the  food  is  kept  between 
the  grinding  surfaces.)  The  tongue  has  functions  in  ad- 
dition to  these  and  is  a  most  useful  organ. 


144 


THE    VITAL   PROCESSES 


3.  The  Muscles  of  Mastication. — These  are  attached  to 
the  lower  jaw  and  bring  about  its  different  movements. 
The  masseter  muscles,  which  are  the  heavy  muscles  in  the 
cheeks,  and  the  temporal  muscles,  located  in  the  region  of 
the  temples,  raise  the  lower  jaw  and  supply  the  force  for 
grinding  the  food.     Small  muscles  situated  below  the  chin 
depress  the  jaw  and  open  the  mouth. 

4.  The  Salivary  Glands. — These  glands  are  situated  in 
the  tissues  surrounding  the  mouth,  and  communicate  with 
it  by  means  of  ducts  (Fig.  67).     They  secrete  the  saliva. 

The  salivary  glands  are  six 
in  number  and  are  arranged 
in  three  pairs.  The  largest, 
called  the  parotid  glands, 
lie,  one  on  either  side,  in 
front  of  and  below  the  ears. 
A  duct  from  each  gland 
passes  forward  along  the 
cheek  until  it  opens  in  the, 
interior  of  the  mouth,  oppo- 
site the  second  molar  tooth 
in  the  upper  jaw.  Next 
FIG.  67. -Salivary  glands  and  the  in  size  to  the  parotids  are 
ducts  connecting  them  with  the  mouth.  ,  ,  •,, 

the      suomaxtllary     glands. 

These  are  located,  one  on  either  side,  just  below  and  in 
front  of  the  triangular  bend  in  the  lower  jaw.  The  smallest 
of  the  salivary  glands  are  the  sublingual.  They  are  situated 
in  the  floor  of  the  mouth,  on  either  side,  at  the  front  and 
base  of  the  tongue.  Ducts  from  the  submaxillary  and 
sublingual  glands  open  into  the  mouth  below  the  tip  of 
the  tongue. 

The  Saliva  and  its  Uses.  —  The  saliva  is  a  transparent 
and  somewhat  slimy  liquid  which  is  slightly  alkaline.     It 


ORGANS   AND   PROCESSES   OF   DIGESTION         145 

consists  chiefly  of  water  (about  99  per  cent),  but  in  this  are 
dissolved  certain  salts  and  an  active  chemical  agent,  or 
enzyme,  called  ptyalin,  which  acts  on  the  starch.  The 
ptyalin  changes  starch  into  a  form  of  sugar  (maltose), 
while  the  water  in  the  saliva  dissolves  the  soluble  portions 
of  the  food.  In  addition  to  this  the  saliva  moistens  and 
lubricates  the  food  which  it  does  not  dissolve,  and  prepares 
it  in  this  way  for  its  passage  to  the  stomach.  The  last  is 
considered  the  most  important  use  of  the  saliva,  and  dry 
substances,  such  as  crackers,  which  require  a  considerable 
amount  of  this  liquid,  cannot  be  eaten  rapidly  without 
choking.  Slow  mastication  favors  the  secretion  and  action 
of  the  saliva. 

•  Deglutition.  —  Deglutition,  or  swallowing,  is  the  process 
by  which  food  is  transferred  from  the  mouth  to  the  stomach. 
Though  this  is  not,  strictly  speaking,  a  digestive  process,  it 
is,  nevertheless,  necessary  for  the  further  digestion  of  the 
food.  Mastication  and  insalivation,  which  are  largely 
mechanical,  prepare  the  food  for  certain  chemical  processes 
by  which  it  is  dissolved.  The  first  of  these  occurs  in  the 
stomach  and  to  this  organ  the  foo,d  is  transferred  from 
the  mouth.  The  chief  organs  concerned  in  deglutition  are 
the  tongue,  the  pharynx,  and  the  esophagus. 

The  Pharynx  is  a  round  and  somewhat  cone-shaped 
cavity,  about  four  and  one  half  inches  in  length,  which 
lies  just  back  of  the  nostrils,  mouth,  and  larynx.  It  is 
remarkable  for  its  openings,  seven  in  number,  by  means 
of  which  it  communicates  with  other  cavities  and  tubes  of 
the  body.  One  of  these  openings  is  into  the  mouth,  one 
into  the  esophagus,  one  into  the  larynx,  and  one  into  each 
of  the  nostrils,  while  two  small  tubes  (the  eustachian)  pass 
from  the  upper  part  of  the  pharynx  to  the  middle  ears. 

The  pharynx  is  the  part  of  the  food  canal  that  is  crossed 


I46  THE   VITAL   PROCESSES 

by  the  passageway  for  the  air.  To  keep  the  food  from 
passing  out  of  its  natural  channel,  the  openings  into  the 
air  passages  have  to  be  carefully  guarded.  This  is  accom- 
plished through  the  soft  palate  and  epiglottis,  which  are 
operated  somewhat  as  valves.  The  muscular  coat  of  the 
pharynx  is  made  up  of  a  series  of  overlapping  muscles 
which,  by  their  contractions,  draw  the  sides  together  and 
diminish  the  cavity.  The  mucous  membrane  lining  the 
pharynx  is  smooth,  like  that  of  the  mouth,  being  covered 
with  a  layer  of  flat  epithelial  cells. 

The  Esophagus,  or  gullet,  is  a  tube  eight  or  nine  inches 
long,  connecting  the  pharynx  with  the  stomach.  It  lies 
for  the  most  part  in  the  thoracic  cavity  and  consists  chiefly 
of  a  thick  mucous  lining  surrounded  by  a  heavy  coat  of 
muscle.  The  muscular  coat  is  composed  of  two  layers  — 
an  inner  layer  whose  fibers  encircle  the  tube  and  an  outer 
layer  whose  fibers  run  lengthwise. 

Steps  in  Deglutition.  —  The  process  of  deglutition  varies  with  the 
kind  of  food.  With  bulky  food  it  consists  of  three  steps,  or  stages, 
as  follows':  i.  By  the  contraction  of  the  muscles  of  the  cheeks,  the 
food  ball,  or  bolus,  is  pressed  into  the  center  of  the  mouth  and  upon 
the  upper  surface  of  the  tongue.  Then  the  tongue,  by  an  upward  and 
backward  movement,  pushes  the  food  under  the  soft  palate  and  into  the 
pharynx. 

2.  As  the  food  passes  from  the  mouth,  the  pharynx  is  drawn  up  to 
receive  it.     At  the  same  time  the  soft  palate  is  pushed  upward  and 
backward,   closing   the   opening  into   the   upper,  pharynx,   while   the 
epiglottis  is  made  to  close  the  opening  into  the  larynx.     By  this  means 
all  communication  between  the  food  canal  and   the   air  passages   is 
temporarily  closed.     The  upper  muscles  of  the  pharynx  now  contract 
upon  the  food,  forcing  it  downward  and  into  the  esophagus. 

3.  In  the  esophagus  the  food  is  forced  along  by  the  successive  con- 
tractions of  muscles,  starting  at  the  upper  end  of  the  tube,  until  the 
stomach  is  reached. 

Swallowing  is  doubtless  aided  to  some  extent  by  the  force  of  gravity. 


ORGANS    AND    PROCESSES    OF   DIGESTION 


147 


That  it  is  independent  of  this  force,  however,  is  shown  by  the  fact  that 
one  may  swallow  with  the  esophagus  in  a  horizontal  position,  as  in  lying 
down. 

The  Stomach.  —  The  stomach  is  the  largest  dilatation  of 
the  alimentary  canal.  It  is  situated  in  the  abdominal  cavity, 
immediately  below  the 
diaphragm,  with  the 
larger  portion  toward 
the  left  side.  Its  connec- 
tion with  the  esophagus 
is  known  as  the  cardiac 
orifice  and  its  opening 
into  the  small  intestine 
is  called  the  pyloric  ori- 
fice. It  varies  greatly  in 
size  in  different  individ- 
uals, being  on  the  aver- 
age from  ten  to  twelve 

,  .,  FIG.  68.  —  Gastric  Glands.     A.   Single 

inches    at    its    greatest  ,  r 

gland  showing   the  two  kinds  of  secreting 

length,  from  four  to  five  cells  and  tne  duct  where  the  gland  opens  on 
inches  at  its  greatest  to  the  surface.  B.  Inner  surface  of  stomach 
Width,  and  holding  from  magnified.  The  small  pits  are  the  openings 
, ,  c  •  .  Tt  from  tne  glands. 

three   to  five  pints.     It 

has  the  coats  common  to  the  canal,  but  these  are  modified 

somewhat  to  adapt  them  to  its  work. 

The  mucous  membrane  of  the  stomach  is  thick  and  highly 
developed.  It  contains  great  numbers  of  minute  tube- 
shaped  bodies,  known  as  the  gastric  glands  (Fig.  68). 
These  are  of  two  general  kinds  and  secrete  large  quanti- 
ties of  a  liquid  called  the  gastric  juice.  When  the  stomach 
is  empty,  the  mucous  membrane  is  thrown  into  folds  which 
run  lengthwise  over  the  inner  surface.  These  disappear, 
however,  when  the  walls  of  the  stomach  are  distended 
with  food. 


I48  THE   VITAL   PROCESSES 

The  muscular  coat  consists  of  three  separate  layers  which 
are  named,  from  the  direction  of  the  fibers,  the  circular 
layer,  the  longitudinal  layer,  and  the  oblique  layer  (Fig.  69). 


Oblique  layer 


—Cardiac  orifice 


Pylorus — 


FIG.  69.  —  Muscles  of  the  stomach  (from  Morris'  Human  Anatomy). 
The  layer  of  longitudinal  fibers  removed. 

The  circular  layer  becomes  quite  thick  at  the  pyloric  orifice, 
forming  a  distinct  band  which  serves  as  a  valve. 

The  outer  coat  of  the  stomach,  called  the  serous  coat,  is  a 
continuation  of  the  peritoneum,  the  membrane  lining  the 
abdominal  cavity. 

Stomach  Digestion.  —  In  the  stomach  begins  the  defi- 
nite work  of  dissolving  those  foods  which  are  insoluble  in 
water.  This,  as  already  stated,  is  a  double  process.  There 
is  first  a  chemical  action  in  which  the  insoluble  are  changed 
into  soluble  substances,  and  this  is  followed  immediately 
by  the  dissolving  action  of  water.  The  chief  substances 
digested  in  the  stomach  are  the  proteids.  These,  in  dis- 
solving, are  changed  into  two  soluble  substances,  known  as 


149 

peptones  and  proteases.  The  digestion  of  the  proteids  is,  of 
course,  due  to  the 

Gastric  Juice. — The  gastric  juice  is  a  thin,  colorless 
liquid  composed  of  about  99  per  cent  of  water  and  about 
i  per  cent  of  other  substances.  The  latter  are  dissolved 
in  the  water  and  include,  besides  several  salts,  three  active 
chemical  agents  —  hydrochloric  acid,  pepsin,  and  rennin. 
Pepsin  is  the  enzyme  which  acts  upon  proteids,  but  it  is 
able  to  act  only  in  an  acid  medium  —  a  condition  which  is 
supplied  by  the  hydrochloric  acid.  Mixed  with  the  hydro- 
chloric acid  it  converts  the  proteids  into  peptones  and 
proteoses. 

Other  Effects  of  the  Gastric  Juice.  —  In  addition  to  di- 
gesting proteids,  the  gastric  juice  brings  about  several 
minor  effects,  as  follows: 

1.  It  checks,  after  a  time,  the  digestion  of  the  starch 
which  was  begun  in  the  mouth  by  the  saliva.1     This  is  due 
to  the  presence  of  the  hydrochloric  acid,  the  ptyalin  being 
unable  to  act  in  an  acid  medium. 

2.  While  there  is  no  appreciable  action  on  the  fat  itself, 
the  proteid  layers  that  inclose  the  fat  particles  are  dissolved 
away  (Fig.  79),  and  the  fat  is  set  free.     By  this  means  the 
fat  is  broken  up  and  prepared  for  a  special  digestive  action 
in  the  small  intestine. 

3.  Dissolved  albumin,  like  that  in  milk,  is  curded,  or 
coagulated,  in  the  stomach.     This  action  is  due  to  the 
rennin.     The    curded    mass   is   then   acted   upon   by   the 
pepsin   and    hydrochloric    acid   in   the   same   manner    as 
the  other  proteids. 


1  The  saliva  may  continue  to  act  for  a  considerable  time  after  the  food  enters  the 
stomach.  "  Careful  examination  of  the  contents  of  the  fundus  (large  end  of  the 
stomach)  by  Cannon  and  Day  has  shown  that  no  inconsiderable  amount  of  salivary 
digestion  occurs  in  the  stomach."  — FISCHER,  The  Physiology  of  Alimentation. 


150 


THE   VITAL  PROCESSES 


4.  The  hydrochloric  acid  acts  on  certain  of  the  insoluble 
mineral  salts  found  in  the  foods  and  reduces  them  to  a 
soluble  condition. 

5.  It  is  also  the  opinion  of  certain  physiologists  that 
cane  sugar  and  maltose  (double  sugars)  are  converted  by 
the  "hydrochloric  .  acid  into  dextrose  and  levulose  (single 
sugars). 

After  a  variable  length  of  time,  the  contents  of  the 
stomach  is  reduced  to  a  rather  uniform  and  pulpy  mass 
which  is  called  chyme.  Portions  of  this  are  now  passed  at 
intervals  into  the  small  intestine. 

Muscular  Action  of  the  Stomach.  —  The  muscles  in  the 
walls  of  the  stomach  have  for  one  of  their  functions  the 
mixing  of  the  food  with  the  gastric  juice.  By  alternately 
contracting  and  relaxing,  the  different  layers  of  muscle 
keep*  the  form  of  the  stomach  changing- — a  result  which 
agitates  and  mixes  its  contents.  This  action  varies  in  dif- 
ferent parts  of  the  organ,  being  slight  or  entirely  absent 
at  the  cardiac  end,  but  quite  marked  at  the  pyloric  end. 

Another  purpose  of  the  muscular  coat  is  to  empty  the 
stomach  into  the  small  intestine.  During  the  greater  part 
of  the  digestive  period  the  muscular  band  at  the  pyloric 
orifice  is  contracted.  At  intervals,  however,  this  band  re- 
laxes, permitting  a  part  of  the  contents  of  the  stomach  to 
be  forced  into  the  small  intestine.  After  the  discharge 
the  pyloric  muscle  again  contracts,  and  so  remains  until 
the  time  arrives  for  another  discharge. 

In  addition  to  emptying  the  st6mach  into  the  small 
intestine,  these  muscles  also  aid  in  emptying  the  organ 
upward  and  through  the  esophagus  and  mouth,  should 
occasion  require.  Vomiting  in  case  of  poisoning,  or  if 
the  food  for  some  reason  fails  to  digest,  is  a  necessary 
though  unpleasant  operation.  It  is  accomplished  by  the 


ORGANS   AND   PROCESSES   OF   DIGESTION         151 

contraction  of  all  the  muscles  of  the  stomach,  together  with 
the  contraction  of  the  walls  of  the  abdomen.  During  these 
contractions  the  pyloric  valve  is  closed,  and  the  muscles  of 
the  esophagus  and  pharynx  are  in  a  relaxed  condition.1 

The  Small  Intestine.  —  This  division  of  the  alimentary 
canal  consists  of  a  coiled  tube,  about  twenty-two  feet  in 
length,  which  occupies  the  cen- 
tral, lower  portion  of  the  abdomi- 
nal   cavity    (Fig.'  71).       At   its 
upper  extremity  it  connects  with 
the  pyloric  end  of  the  stomach 
(Fig.  70),  and  at  its  lower  end  it 
joins    the    large    intestine.       It 
averages  a  little  over  an  inch  in        FIG;  70._  Passage    from 
diameter,   and    gradually  dimin-    stomach   into  small   intestine. 

isheS  in  Size  from  the  Stomach  Illustration  also  shows  arrange- 
to  the  large  intestine.  The  first  ™ent  of  mucous  T^T  in 

the  two  organs.     D.  Bile  duct. 

eight  or  ten  inches  form  a  short 

curve,  known  as  the  duodenum.  The  upper  two  fifths  of 
the  remainder  is  called  the  jejunum,  and  the  lower  three 
fifths  is  known  as  the  ileum.  The  ileum  joins  that  part  of 
the  large  intestine  known  as  the  caecum,  and  at  their  place 
of  union  is  a  marked  constriction  which  prevents  material 
from  passing  from  the  large  into  the  small  intestine  (Fig. 
73).  This  is  known  as  the  ileo-ccecal  valve. 

The  mucous  membrane  of  the  small  intestine  is  richly 
supplied  with  blood  vessels  and  contains  glands  that  secrete 

1  Perhaps  the  simplest  method  of  inducing  vomiting  is  that  of  thrusting  a  finger 
down  the  throat.  To  make  this  method  effective  the  finger  should  be  held  in  the 
throat  until  the  vomiting  begins.  An  emetic,  such  as  a  glass  of  lukewarm  salt 
water  containing  a  teaspoonful  of  mustard,  should  also  be  taken,  and,  in  the  case 
of  having  swallowed  poison,  the  vomiting  should  be  repeated  several  times.  It 
may  even  be  advantageous  to  drink  water  and  then  vomit  it  up  in  order  to  wash 
out  the  stomach. 


152 


THE   VITAL   PROCESSES 


a  digestive  fluid  known  as  the  intestinal  juice.  The  mem- 
brane is  thrown  into  many  transverse,  or  circular,  folds 
which  increase  its  surface  and  also  prevent  materials  from 
passing  too  rapidly  through  the  intestine.  One  important 
respect  in  which  the  small  intestine  differs  from  all  other 
portions  of  the  food  canal  is  that  its  surface  is  covered  with 
great  numbers  of  minute  elevations  known  as  the  villi. 
The  purpose  of  these  is  to  aid  in  the  absorption  of  the 
nutrients  as  they  become  dissolved  (Chapter  XI). 

The  muscular  coat  of  the  small  intestine  is  made  up  of  two 
distinct  layers  —  the  inner  layer  consisting  of  circular  fibers 
and  the  outer  of  longitudinal  fibers.  These  muscles  keep 
the  food  materials  mixed  with  the  juices  of  the  small  intes- 
tine, but  their  main  purpose  is  to  force  the  materials  under- 
going digestion  through  this  long  and  much-coiled  tube. 

The  outer,  or  serous,  coat  of  the  small  intestine,  like  that 
of  the  stomach,  is  an  extension  from  the  general  lining  of 
the  abdominal  cavity,  or  peritoneum.  In  fact,  the  intestine 
lies  in  a  fold  of  the  peritoneum,  somewhat  as  an  arm  in  a 
sling,  while  the  peritoneum,  by  connecting  with  the  back 
wall  of  the  abdominal  cavity,  holds  this  great  coil  of  digest- 
ive tubing  in  place  (Fig.  64).  The  portion  of  the  peri- 
toneum which  attaches  the  intestine  to  the  wall  of  the 
abdomen  is  called  the  mesentery. 

Most  of  the  liquid  acting  on  the  food  in  the  small  intes- 
tine is  supplied  by  two  large  glands,  the  liver  and  the  pan- 
creas, that  connect  with  it  by  ducts. 

The  Liver  is  situated  immediately  below  the  diaphragm, 
on  the  right  side  (Figs.  71  and  72),  and  is  the  largest  gland 
in  the  body.  It  weighs  about  four  pounds  and  is  separated 
into  two  main  divisions,  or  lobes.  It  is  complex  in  struc- 
ture and  differs  from  the  other  glands  in  several  particulars. 
It  receives  blood  from  two  distinct  sources — the  portal  vein 


ORGANS    AND   PROCESSES    OF    DIGESTION         153 


FIG.  71.  —  Abdominal  cavity  with  organs  of  digestion  in  position. 


154 


THE   VITAL   PROCESSES 


and  the  hepatic  artery.  The.  portal  vein  collects  the  blood 
from  the  stomach,  intestines,  and  spleen,  and  passes  it  to 
the  liver.  This  blood  is  loaded  with  food  materials,  but 
contains  little  or  no  oxygen.  The  hepatic  artery,  which 
branches  from  the  aorta,  carries  to  the  liver  blood  rich  in 
oxygen.  In  the  liver  the  portal  vein  and  the  hepatic 

artery  divide  and  sub- 
divide, and  finally  empty 
their  blood  into  a  single 
system  of  capillaries  sur- 
rounding the  liver  cells. 
These  capillaries  in  turn 
empty  into  a  single  sys- 
tem of  veins  which,  unit- 
ing to  form  the  hepatic 
veins  (two  or  three  in 
number),  pass  the  blood 
into  the  inferior  vena 
cava  (Fig.  72). 

The     liver     secretes 
daily  from  one   to   two 
pounds  of  a  liquid  called 
FIG.  72.  — Relations  of  the  liver.    Dia-    ^le.      A    reservoir    for 

gram  showing  the  connection  of  the  liver  the  bile  is  provided  by 
with  the  large  blood  vessels  and  the  food  a  smSL\\f  membranous 

sack,    called     the    gall 

bladder,  located  on  the  underside  of  the  liver.  The  bile 
passes  from  the  gall  bladder,  and  from  the  right  and  left 
lobes  of  the  liver,  by  three  separate  ducts.  These  unite  to 
form  a  common  tube  which,  uniting  with  the  duct  from  the 
pancreas,  empties  into  the  duodenum.  Though  usually 
described  as  a  digestive  gland,  the  liver  has  other  func- 
tions of  equal  or  greater  importance  (Chapter  XIII). 


ORGANS   AND   PROCESSES    OF    DIGESTION         155 

The  Bile  is  a  golden  yellow  liquid,  having  a  slightly 
alkaline  reaction  and  a  very  bitter  taste.  It  consists,  on 
the  average,  of  about  97  per  cent  of  water  and  3  per  cent 
of  solids.1  The  solids  include  bile  pigments,  bile  salts,  a 
substance  called  cholesterine,  and  mineral  salts.  The 
pigments  (coloring  matter)  of  the  bile  are  derived  from  the 
hemoglobin  of  broken-down  red  corpuscles  (page  27). 

Much  about  the  composition  of  the  bile  is  not  under- 
stood. It  is  known,  however,  to  be  necessary  to  digestion, 
its  chief  use  being  to  aid  in  the  digestion  and  absorption  of 
fats.  It  is  claimed  also  that  the  bile  aids  the  digestive  pro- 
cesses in  some  general  ways  —  counteracting  the  acid  of 
the  gastric  juice,  preventing  the  decomposition  of  food 
in  the  intestines,  and  stimulating  muscular  action  in  the 
intestinal  walls;  No  enzymes  have  been  discovered  in 
the  bile. 

The  Pancreas  is  a  tapering  and  somewhat  wedge-shaped 
gland,  and  is  so  situated  that  its  larger  extremity,  or  head, 
is  encircled  by  the  duodenum.  From  here  the  more 
slender  portion  extends  across  the  abdominal  cavity  nearly 
parallel  to  and  behind  the  lower  part  of  the  stomach.  It 
has  a  length  of  six  or  eight  inches  and  weighs  from  two 
to  three  and  one  half  ounces.  Its  secretion,  the  pancreatic 
juice,  is  emptied  into  the  duodenum  by  a  duct  which,  as  a 
rule,  unites  with  the  duct  from  the  liver. 

The  Pancreatic  Juice  is  a  colorless  and  rather  viscid 
liquid,  having  an  alkaline  reaction.  It  consists  of  about 
97.6  per  cent  of  water  and  2.4  per  cent  of  solids.  The 
solids  include  mineral  salts  (the  chief  of  which  is  sodium 
carbonate)  and  four  different  chemical  agents,  or  enzymes, 
—  trypsin,  amylopsin,  steapsin,  and  a  milk-curding  enzyme. 
These  active  constituents  make  of  the  pancreatic  juice  the 

1  Hammerstein,   Text-book  of  Physiological  Chemistry. 


I56  THE    VITAL    PROCESSES 

most  important  of  the  digestive  fluids.  It  acts  with  vigor 
on  all  of  the  nutrients  insoluble  in  water,  producing  the 
following  changes  : 

1.  It  converts  the  starch  into  maltose,  completing  the 
work  begun  by  the    saliva.     This   action   is    due   to   the 
amylopsin?-    which    is    similar    to    ptyalin    but    is    more 
vigorous. 

2.  It   changes    proteids   into    peptones   and   proteoses, 
completing  the  work  begun  by  the  gastric  juice.     This  is 
accomplished  by  the  trypsin,  which  is  similar  to,  but  more 
active  than,  the  pepsin. 

3.  It  digests  fat.     In  this  work  the  active  agent  is  the 
steapsin. 

The  necessity  of  a  milk-curding  enzyme,  somewhat 
similar  to  the  rennin  of  the  gastric  juice,  is  not  under- 
stood. 

Digestion  of  Fat.  —  Several  theories  have  been  proposed 
at  different  times  regarding  the  digestion  and  absorption 
of  fat.  Among  these,  what  is  known  as  the  "  solution 
theory  "  seems  to  have  the  greatest  amount  of  evidence 
in  its  favor.  According  to  this  theory,  the  fat,  under  the 
influence  of  the  steapsin,  absorbs  water  and  splits  into  two 
substances,  recognized  as  glycerine  and  fatty  acid.  This 
finishes  the  process  so  far  as  the  glycerine  is  concerned, 
as  this  is  soluble  in  water ;  but  the  fatty  acid,  which  (from 
certain  fats)  is  insoluble  in  water,2  requires  further  treat- 
ment. The  fatty  acid  is  now  supposed  to  "be  acted  on  in 
one,  or  both,  of  the  following  ways  :  I.  To  be  dissolved  as 
fatty  acid  by  the  action  of  the  bile  (since  bile  is  capable 

1Amylopsin  is  absent  from  the  pancreatic  juice  of  infants,  a  condition  which 
shows  that  milk  and  not  starch  is  their  natural  food. 

2  The  fact  that  butter  is  more  easily  digested  than  other  fatty  substances  is 
probably  due  to  its  consisting  largely  of  a  kind  of  fat  which,  on  splitting,  forms  a 
fatty  acid  (butyric)  which  is  soluble  in  water. 


ORGANS   AND   PROCESSES   OF   DIGESTION         157 

of  dissolving  it  under  certain  conditions).  2.  To  be  con- 
verted by  the  sodium  carbonate  into  a  form  of  soap  which 
is  soluble  in  water. 

The  emulsification  of  fat  is  known  to  occur  in  the  small  intestine. 
By  this  process  the  fat  is  separated  into  minute  particles  which  are  sus- 
pended in  water,  but  not  changed  chemically,  the  mixture  being  known 
as  an  emulsion.  While  this  is  believed  by  some  to  be  an  actual  process 
of  digestion,  the  advocates  of  the  solution  theory  claim  that  it  is  a  pro- 
cess accompanying  and  aiding  the  conversion  of  fat  into  fatty  acid  and 
glycerine.1 

The  Intestinal  Juice  is  a  clear  liquid  with  an  alkaline 
reaction,  containing  water,  mineral  salts,  and  certain  proteid 
substances  that  may  act  as  enzymes.  It  assists  in  bring- 
ing about  an  alkaline  condition  in  the  small  intestine  and 
aids  in  the  reduction  of  cane  sugar  and  maltose  to  the  sim- 
ple sugars,  dextrose  and  levulose.  Since  it  is  difficult  to 
obtain  this  liquid  in  sufficient  quantities  for  experimenting, 
its  uses  have  not  been  fully  determined.  Recent  investi- 
gators, however,  assign  to  it  an  important  place  in  the 
work  of  digestion. 

Work  of  the  Small  Intestine.  —  The  small  intestine  is 
the  most  important  division  of  the  alimentary  canal.  It 
serves  as  a  receptacle  for  holding  the  food  while  it  is  being 
acted  upon ;  it  secretes  the  intestinal  juice  and  mixes  the 
food  with  the  digestive  fluids ;  it  propels  the  food  toward 
the  large  intestine;  and,  in  addition  to  all  this,  serves  ^s 
an  organ  of  absorption. 

Digestion  is  practically  finished  in  the  small  intestine, 
and  a  large  portion  of  the  reduced  food  is  here  absorbed. 
There  is  always  present,  however,  a  variable  amount  of 
material  that  is  not  digested.  This,  together  with  a  con- 
siderable volume  of  liquid,  is  passed  into 

1  Fischer,  Physiology  of  Alimentation. 


158 


THE   VITAL   PROCESSES 


The  Large  Intestine.  —  The  large  intestine  is  a  tube  from 
five  to  six  feet  in  length  and  averaging  about  one  and  one 
half  inches  in  diameter.  It  begins  at  the  lower  right  side 
of  the  abdominal  cavity,  forms  a  coil  which  almost  com- 
pletely surrounds  the  coil  of  small  intestine,  and  finally 

terminates  at  the  surface  of 
the  body  (Figs.  2,  71  and  73). 
It  has  three  divisions,  known 
as  the  caecum,  the  colon,  and 
the  rectum. 

The  ccecum  is  the  pouch- 
like  dilatation  of  the  large 
intestine  which  receives  the 
lower  end  of  the  small  in- 
testine. It  measures  about 
two  and  one  half  inches  in 
diameter  and  has  extending 
from  one  side  a  short,  slender, 
and  blind  tube,  called  the 
vermiform  appendix.  This  structure  serves  no  purpose 
in  digestion,  but  appears  to  be  the  rudiment  of  an  organ 
which  may  have  served  a  purpose  at  some  remote  period 
in  the  history  of  the  human  race.  The  caecum  gradually 
blends  into  the  second  division  of  the  large  intestine, 
called  the  colon. 

ikThe  colon  consists  of  four  parts,  described  as  the  as- 
cending colon,  the  transverse  colon,  the  descending 
colon,  and  the  sigmoid  flexure,  or  sigmoid  colon.  The 
first  three  divisions  are  named  from  the  direction  of  the 
movement  of  materials  through  them  and  the  last  from 
its  shape,  which  is  similar  to  that  of  the  Greek  letter 
sigma  (2). 

The  rectum  is  the  last  division  of   the  large  intestine 


FIG.  73.  —  Passage  from  small 
into  large  intestine.  At  the  ileo- 
caecal  valve  is  the  narrowest  constric- 
tion of  the  food  canal. 


ORGANS   AND   PROCESSES   OF   DIGESTION         159 

It  is  a  nearly  straight  tube,  from  six  to  eight  inches  in 
length,  and  connects  with  the  external  surface  of  the  body. 
The  general  structure  of  the  large  intestine  is  similar  to 
that  of  the  small  intestine,  and,  like  the  small  intestine,  it 
is  held  in  place  by  the  peritoneum.  It 
differs  from  the  small  intestine,  how- 
ever, in  its  lining  of  mucous  membrane 
and  in  the  arrangement  of  the  muscular 
coat.  The  mucous  membrane  presents 
a  smooth  appearance  and  has  no  villi, 
while  the  longitudinal  layer  of  the  mus- 
cular coat  is  limited  to  three  narrow 
,  ,  ,  .  FIG.  74.  —  Section 

bands   that   extend    along    the   greater  of    large    intestinej 

length  of  the  tube  (Fig.  74).      These  showing  the  coats,    i. 
bands  are  shorter  than  the  coats,  and  Serous  coat.     2.  Cir- 

draw  the  large  intestine  into  a  number  cula'  ^yer  of  muscle' 

f    u    11  u        v.        u-   u  -4.  •  j-i       3'    Submucous     coat- 

of  shallow  pouches,  by  which  it  is  readily  4   Mucous  membrane. 

distinguished  from  the  small  intestine  5.  Muscular  bands  ex- 

(Fig-    71 Y  .      tending     lengthwise 

'  Work  of  the  Large  Intestine.  -  The  over  the  intestine" 
large  intestine  serves  as  a  receptacle  for  the  materials  from 
the  small  intestine.  The  digestive  fluids  from  the  small 
intestine  continue  their  action  here,  and  the  dissolved 
materials  also  continue  to  be  absorbed.  In  these  respects 
the  work  of  the  large  intestine  is  similar  to  that  of  the 
small  intestine.  It  does,  however,  a  work  peculiar  to  itself 
in  that  it  collects  and  retains  undigested  food  particles, 
together  with  other  wastes,  and  ejects  them  periodically 
from  the  canal. 

Work  of  the  Alimentary  Muscles.  —  The  mechanical 
part  of  digestion  is  performed  by  the  muscles  that  encircle 
the  food  canal.  Their  uses,  which  have  already  been 
mentioned  in  connection  with  the  different  organs  of 


160  THE  VITAL   PROCESSES 

digestion,  may  be  here  summarized:  They  supply  the 
necessary  force  for  masticating  the  food.  They  propel 
the  food  through  the  canal.  They  mix  the  food  with  the 
different  juices.  At  certain  places  they  partly  or  com- 
pletely close  the  passage  until  a  digestive  process  is  com- 
pleted. They  may  even  cause  a  reverse  movement  of  the 
food,  as  in  vomiting.  All  of  the  alimentary  muscles,  except 
those  around  the  mouth,  are  involuntary.  Their  work  is 
of  the  greatest  importance. 

Other  Purposes  of  the  Digestive  Organs.  —  The  digestive  organs  serve 
other  important  purposes  besides  that  of  dissolving  the  foods.  They 
provide  favorable  conditions  for  passing  the  dissolved  material  into  the 
blood.  They  dispose  of  such  portions  of  the  foods  as  fail,  in  the  di- 
gestive processes,  to  be  reduced  to  a  liquid  state.  A  considerable 
amount  of  waste  material  is  also  separated  from  the  blood  by  the  glands 
of  digestion  (especially  the  liver),  and  this  is  passed  from  the  body  with 
the  undigested  portions  of  food.  Then  the  food  canal  (stomach  in 
particular)  is  a  means  of  holding,  or  storing,  food  which  is  awaiting  the 
processes  of  digestion.  Considering  the  number  of  these  purposes,  the 
digestive  organs  are  remarkably  simple,  both  in  structure  and  in  method 
of  operation. 

HYGIENE  OF  DIGESTION 

Many  of  the  ills  to  which  flesh  is  heir  are  due  to  im- 
proper methods  of  taking  food  and  are  cured  by  observ- 
ing the  simple  rules  of  eating.  Habit  plays  a  large  part 
in  the  process  and  children  should,  for  this  reason,  be 
taught  early  to  eat  properly.  Since  the  majority  of  the 
digestive  processes  are  involuntary  and  the  food,  after  being 
swallowed,  is  practically  beyond  control,  careful  attention 
must  be  given  to  the  proper  mastication  of  the  food  and 
to  such  other  phases  of  digestion  as  are  under  control. 

Necessity  for  Thorough  Mastication.  —  Mastication  pre- 
pares the  food  for  the  digestive  processes  which  follow. 
Unless  the  food  has  been  properly  masticated,  the  di- 


ORGANS    AND    PROCESSES    OF    DIGESTION         161 

gestive  fluids  in  the  stomach  and  intestines  cannot  act 
upon  it  to  the  best  advantage.  When  the  food  is  carefully 
chewed,  a  larger  per  cent  of  it  is  actually  digested  — a  point 
of  importance  where  economy  in  the  use  of  food  needs  to 
be  practiced. 

A  fact  not  to  be  overlooked  is  that  one  cannot  eat 
hurriedly  and  practice  thorough  mastication.  The  food 
must  not  be  swallowed  in  lumps,  but  reduced  to  a  finely 
divided  and  pulpy  mass.  This  requires  time.  The  one 
who  hurries  through  the  meal  is  necessarily  compelled  to 
bolt  his  food.  Thirty  minutes  is  not  too  long  to  give  to  a 
meal,  and  a  longer  period  is  even  better. 

Perhaps  the  most  important  result  of  giving  plenty  of 
time  to  the  taking  of  food  is  that  of  stimulating  the  di- 
gestive glands  to  a  proper  degree  of  activity.  That  both  the 
salivary  and  gastric  glands  are  excited  by  the  sight,  smell, 
and  thought  of  food  and,  through  taste,  by  the  presence 
of  food  in  the  mouth,  has  been  fully  demonstrated.  Food 
that  is  thoroughly  masticated  and  relished  will  receive 
more  saliva  and  gastric  juice,  and  probably  more  of  other 
juices,  than  if  hastily  chewed  and  swallowed.  This  has  a 
most  important  bearing  upon  the  efficiency  of  the  digestive 
processes. 

Order  of  Taking  Food.  —  There  has  been  evolved  through  experience 
a  rather  definite  order  of  taking  food,  which  our  knowledge  of  the 
process  of  digestion  seems  to  justify.  The  heavy  foods  (proteids  for 
the  most  part)  are  eaten  first ;  after  which  are  taken  starchy  foods  and 
fats;  and  the  meal  is  finished  off  with  sweetmeats  and  pastry.1  The 
scientific  arguments  for  this  order  are  the  following : 

I .    By  receiving  the  first  of  the  gastric  flow  the  proteids  can  begin 

1  Beginning  the  meal  with  a  little  soup,  as  is  frequently  done,  may  be  of  slight 
advantage  in  stimulating  the  digestive  glands.  To  serve  this  purpose,  however, 
and  not  interfere  with  the  meal  proper,  it  should  contain  little  greasy  or  starchj 
material  and  should  be  taken  in  small  amount. 


j62  THE   VITAL   PROCESSES 

digesting  without  delay.  Since  these  are  the  main  substances  acted  on 
in  the  stomach,  the  time  required  for  their  digestion  is  shortened  by 
eating  them  first. 

2.  Sugar,  being  of  the  nature  of  predigested  starch,  quickly  gets  into 
the  blood  and  satisfies  the  relish  for  food.     The  result  of  taking  sugar 
first  may  be  to  cause  one  to  eat  less  than  he  needs  and  to  diminish  the 
activity  of  the  glands. 

3.  Fat  or  grease,  if  taken  first,  tends  to  form  a  coating  over  the 
walls  of  the  stomach  and  around  the  material  to  be  digested.     This 
prevents  the  juices  from  getting  to  and  mixing  with  the  foods  upon 
which  they  are  to  act. 

4.  Starch  following  the  proteids,  for  the  most  part,  does  not  so 
quickly  come   in  contact   with   the  gastric  juice.     This   enables   the 
ptyalin  of  the  saliva  to  continue  its  action  for  a  longer  time  than  if 
the  starch  were  eaten  first. 

Liquids  during  the  Meal.  —  Liquids  as  ordinarily  taken 
during  the  meal  are  objectionable.  They  tend  to  diminish 
the  secretion  of  the  saliva  and  to  cause  rapid  eating. 
Instead  of  eating  slowly  and  swallowing  the  food  only  so 
fast  as  the  glands  can  supply  the  necessary  saliva,  the 
liquid  is  used  to  wash  the  food  down.  Water  or  other 
drinks  should  be  taken  after  the  completion  of  the  meal 
or  when  the  mouth  is  completely  free  from  food.  Even 
then  it  should  be  taken  in  small  sips.  While  the  taking  of 
a  small  amount  of  water  in  this  way  does  no  harm,  a  large 
volume  has  the  effect  of  weakening  the  gastric  juice. 
Most  of  the  water  needed  by  the  body  should  be  taken 
between  meals. 

The  State  of  Mind  has  much  to  do  with  the  proper  diges- 
tion of  the  food.  Worry,  anger,  fear,  and  other  disturbed 
mental  states  are  known  to  check  the  secretion  of  fluids 
and  to  interfere  with  the  digestive  processes.  While  the 
cultivation  of  cheerfulness  is  important  for  its  general 
hygienic  effects,  it  is  of  especial  value  in  relation  to  diges- 
tion. Intense  emotions,  either  during  or  following  the 


ORGANS    AND   PROCESSES   OF   DIGESTION         163 

meal,  should  if  possible  be  avoided.  The  table  is  no  place 
for  settling  difficulties  or  administering  rebuke.  The  con- 
versation, on  the  other  hand,  should  be  elevating  and  joy 
giving,  thereby  inducing  a  desirable  reactionary  influence 
upon  the  digestive  processes. 

Care  of  the  Teeth.  —  The  natural  teeth  are  indispensable 
for  the  proper  mastication  of  the  food.  Of  especial  value 
are  the  molars  —  the  teeth  that  grind  the  food.  The  de- 
velopment of  the  profession  of  dentistry  has  made  possible 
the  preservation  of  the  teeth,  even  when  naturally  poor, 
as  long  as  one  has  need  of  them.  To  preserve  the  teeth 
they  must  be  kept  clean.  They  should  be  washed  at  least 
once  a  day  with  a  soft-bristled  brush,  and  small  particles 
of  food,  lodged  between  them,  should  be  removed  with  a 
wooden  pick.  The  biting  of  hard  substances,  such  as 
nuts,  should  be  avoided,  on  account  of  the  danger  of 
breaking  the  enamel,  although  the  chewing  of  tough  sub- 
stances is  considered  beneficial. 

Decayed  places  in  the  teeth  should  be  promptly  filled 
by  the  dentist.  It  is  well,  even  when  decayed  places  are 
not  known  to  exist,  to  have  the  teeth  examined  occasionally 
in  order  to  detect  such  places  before  they  become  large. 
On  account  of  the  expense,  pain,  and  inconvenience  there 
is  a  tendency  to  put  off  dental  work  which  one  knows 
ought  to  be  done.  Perhaps  in  no  other  instance  is  pro- 
crastination so  surely  punished.  The  decayed  places 
become  larger  and  new  points  of  decay  are  started ; 
and  the  pain,  inconvenience,  and  expense  are  increased 
proportionately. 

The  Natural  Appetite  should  be  followed  with  reference 
to  both  the  kind  and  the  amount  of  food  eaten.  No 
system  of  knowledge  will  ever  be  devised  which  can 
replace  the  appetite  as  an  aid  in  the  taking  of  food.  //  h 


!64  THE   VITAL   PROCESSES 

nature  s  means  of  indicating  the  needs  of  the  body.  The 
natural  appetite  may  be  spoiled,  however,  by  overeating 
and  by  the  use  of  highly  seasoned  foods,  or  by  indulging 
in  stimulants  during  the  meal.  It  is  spoiled  in  children 
by  too  free  indulgence  in  sweetmeats.  By  cultivating 
the  natural  appetite  and  heeding  its  suggestions,  one  has 
at  his  command  an  almost  infallible  guide  in  the  taking 
of  food. 

Preparation  of  Meals.  —  The  cooking  of  food  serves 
three  important  purposes.  It  renders  the  food  more 
digestible,  relieving  the  organs  of  unnecessary  work;  it 
destroys  bacteria  that  may  be  present  in  the  food,  di- 
minishing the  likelihood  of  introducing  disease  germs  into 
the  body ;  and  it  makes  the  food  more  palatable,  thereby 
supplying  a  necessary  stimulus  to  the  digestive  glands. 
While  the  methods  employed  in  the  preparation  of  the 
different  foods  have  much  to  do  with  the  ease  with  which 
they  are  digested  and  with  their  nourishing  qualities,  the 
scope  of  our  subject  does  not  permit  of  a  consideration  of 
these  methods. 

Quantity  of  Food.  —  Overeating  and  undereating  are 
both  objectionable  from  a  hygienic  standpoint.  Over- 
eating, by  introducing  an  unnecessary  amount  of  food  into 
the  body,  overworks  the  organs  of  digestion  and  also  the 
organs  of  excretion.  It  may  also  lead  to  the  accumulation 
of  burdensome  fat  and  of  harmful  wastes.  On  the  other 
hand,  the.  taking  of  too  little  food  impoverishes  the  blood 
and  weakens  the  entire  body.  As  a  rule,  however,  more 
people  eat  too  much  than  too  little,  and  to  quit  eating 
before  the  appetite  is  fully  satisfied  is  with  many  persons 
a  necessary  precaution.  The  power  of  self-control,  valu- 
able in  all  phases  of  life,  is  indispensable  in  the  avoidance 
of  overeating. 


ORGANS   AND   PROCESSES   OF   DIGESTION         165 

Frequency  of  Taking  Food.  —  Eating  between  meals  is 
manifestly  an  unhealthful  practice.  The  question  has 
also  been  raised  as  to  whether  the  common  habit  of  eating 
three  times  a  day  is  best  suited  to  all  classes  of  people. 
Many  people  of  weak  digestive  organs  have  been  bene- 
fited by  the  plan  of  two  meals  a  day,  while  others  adopt 
the  plan  of  eating  one  heavy  meal  and  two  light  ones. 
Either  plan  gives  the  organs  of  digestion  more  time  to 
rest  and  diminishes  the  liability  of  overeating.  On  the 
other  hand,  those  doing  heavy  muscular  work  can  hardly 
derive  the  energy  which  they  need  from  less  than  three 
good  meals  a  day.  Though  no  definite  rule  can  be  laid 
down,  there  is  involved  a  hygienic  principle  which  all 
should  follow :  Meals  should  not  overlap.  The  stomach 
should  be  free  from  food  taken  at  a  previous  meal  before 
more  is  introduced  into  it.  When  this  principle  is  not 
observed,  material  ferments  in  the  stomach,  causing  indi- 
gestion and  other  disorders.  It  should  be  noted,  however, 
that  the  overlapping  may  be  due  to  overeating  as  well  as 
to  eating  too  frequently. 

Dangers  from  Impure  Food.  —  Food  is  frequently  the 
carrier  of  disease  germs  and  for  this  reason  requires  close 
inspection  (page  128).  Typhoid  fever,  a  most  dangerous 
disease,  is  usually  contracted  through  either  impure  food  or 
impure  water  (Chapter  XXIII).  One  safeguard  against 
disease  germs,  as  stated  above,  is  thorough  cooking.  Too 
much  care  cannot  be  exercised  with  reference  to  the  water 
for  drinking  purposes.  Water  which  is  not  perfectly  clear, 
which  smells  of  decaying  material,  or  which  forms  a  sedi- 
ment on  standing  is  usually  not  fit  to  drink.  It  can,  how- 
ever, be  rendered  comparatively  harmless  by  boiling.  The 
objections  which  many  people  have  to  drinking  boiled 
water  are  removed  when  it  is  boiled  the  day  before  it  is 


r66  THE  VITAL  PROCESSES 

used,  so  as  to  give  it  time  to  cool,  settle,  and  replace  the  ait 
driven  off  by  the  boiling. 

Care  of  the  Bowels.  —  In  considering  the  hygiene  of 
the  alimentary  canal,  the  fact  that  it  is  used  as  a  means 
of  separating  the  impurities  from  the  body  must  not  be 
overlooked.  Frequently,  through  lack  of  exercise,  negli- 
gence in  evacuating  the  bowels,  or  other  causes,  a  weak- 
ened condition  of  the  canal  is  induced  which  results  in  the 
retention  of  impurities  beyond  the  time  when  they  should 
be  discharged.  This  is  a  great  annoyance  and  at  the  same 
time  a  menace  to  the  health. 

In  most  cases  this  condition  can  be  relieved,  and  pre- 
vented from  recurring,  by  observing  the  following  habits : 
i.  Have  a  regular  time  each  day  for  evacuating  the  bowels. 
This  is  a  most  important  factor  in  securing  the  necessary 
movements.  2.  Drink  a  cup  of  cold  water  on  rising  in  the 
morning  and  on  retiring  at  night.  3.  Eat  generously  of 
fruits  and  other  coarse  foods,  such  as  corn  bread,  oatmeal, 
hominy,  cabbage,  etc.  4.  Practice  persistently  such  exer- 
cises as  bring  the  abdominal  muscles  into  play.  These 
exercises  strengthen  indirectly  the  muscles  of  the  canal. 
5.  Avoid  overwork,  especially  of  the  nervous  system. 

Alcohol  and  Digestion.  —  Though  exciting  temporarily  a 
greater  flow  of  the  digestive  fluids,  alcoholic  drinks  taken 
in  any  but  very  small  quantities  are  considered  detrimental 
to  the  work  of  digestion.  Large  doses  retard  the  action 
of  enzymes,  inflame  the  mucous  lining  of  the  stomach,1  and 

1  Dr.  William  Beaumont,  an  American  surgeon  of  the  last  century,  made  a  series 
of  observations  upon  a  human  stomach  (that  of  Alexis  St.  Martin)  having  an  arti- 
ficial opening,  the  result  of  a  gunshot  wound.  Much  of  our  knowledge  of  the 
digestion  of  different  foods  was  obtained  through  these  observations.  In  spite  of 
the  protests  of  his  physician,  St.  Martin  would  occasionally  indulge  in  strong  drink 
and  always  with  the  same  result  —  the  lining  of  the  stomach  became  much  inflamed 
and  very  sensitive.and  the  natural  processes  of  digestion  were  temporarily  suspended. 


ORGANS    AND    PROCESSES    OF    DIGESTION         167 

bring  about  a  diseased  condition  of  the  liver.  It  may  be 
noted,  however,  that  the  bad  effects  of  alcoholic  beverages 
upon  the  stomach,  the  liver,  and  the  body  in  general  are 
less  pronounced  when  these  are  taken  as  a  part  of  the 
regular  meals. 

Effects  of  Tea  and  Coffee.  —  In  addition  to  the  stimulating 
agent  caffeine,  tea  and  coffee  contain  a  bitter,  astringent 
substance,  known  as  tannin.  On  account  of  the  tannin 
these  beverages  tend  to  retard  digestion  and  to  irritate  the 
lining  of  the  stomach  —  effects  that  may  be  largely  obviated 
by  methods  of  preparing  tea  and  coffee  which  dissolve 
little  of  the  tannin.  (They  should  be  made  without  con- 
tinued boiling  or  steeping.)  The  caffein  may  do  harm* 
through  its  stimulating  effect  upon  the  nervous  system 
(page  56)  and  through  the  introduction  of  a  special  waste 
into  the  body.  In  chemical  composition  caffeine  closely 
resembles  a  waste,  called  uric  acid,  and  in  the  body  is  con- 
verted into  this  substance.  If  one  is  in  a  weakened  condi- 
tion, the  uric  acid  may  fail  to  be  oxidized  to  urea,  as  occurs 
normally,  or  to  be  thrown  off  as  uric  acid.  In  this  case  it 
accumulates  *in  the  body,  causing  rheumatism  and  related 
diseases.  It  thus  happens  that  while  some  people  may 
use  tea  and  coffee  without  detriment,  others  are  injured 
by  them. 

Summary.  —  The  main  structure  in  the  digestive  system 
is  the  alimentary  canal.  This  provides  cavities  where 
important  dissolving  processes  take  place,  and  tubes  for 
joining  these  cavities,  while  glands  connecting  with  the 
canal  supply  the  necessary  liquids  for  changing  and  dissolv- 
ing the  foods.  The  general  plan  of  digestion  is  that  of  pass- 
ing the  food  through  the  canal,  beginning  with  the  mouth,  and 
of  acting  on  it  at  various  places,  with  the  final  result  of  re- 
ducing most  of  it  to  the  liquid  state.  The  digestive  fluids 


168  THE   VITAL   PROCESSES 

supply  water  which  acts  as  a  solvent  and  carries  the  active 
chemical  agents,  or  enzymes,  that  convert  the  insoluble 
foods  into  substances  that  are  soluble.  The  muscles  in 
the  walls  of  the  canal  perform  the  mechanical  work  of 
digestion,  while  the  nervous  system  controls  and  regulates 
the  activity  of  the  various  organs  concerned  in  this  work. 

Exercises.  —  I.  State  the  general  purpose  of  digestion.  How  does 
digested  food  differ  from  that  not  digested  ? 

2.  Name  all  the  divisions  of  the  alimentary  canal  in  the  order  in 
which  the  food  passes  through  them. 

3.  What  other  work  besides  digestion  is  carried  on  by  the  alimentary 
canal ? 

4.  What  is  gained  by  the  mastication  of  the  food  ?     Why  should 
mastication  precede  the  other  processes  of  digestion  ? 

5.  What  is  the  work  of  the  tongue  in  digestion  ? 

6.  State  the  purposes  served  by  the  gastric  juice. 

7.  Give  reasons  for  regarding  the  small  intestine  as  the  most  im- 
portant division  of  the  food  canal. 

8.  At»what  places,  and  by  the  action  of  what  liquids,  are  fats,  pro- 
teids,  and  starch  digested  ? 

9.  What  enzymes  are  found  in  the  pancreatic  juice  ?     What  is  the 
digestive  action  of  each  ? 

10.  Describe  the  work  performed  by  the  muscles  of  the  stomach,  the 
mouth,  the  esophagus,  and  the  small  intestine. 

n.   What' advantages  are  derived  from  the  use  of  cooked  food  ? 

12.  State  the  advantages  of  drinking  pure  water. 

13.  If  all  the  food  that  one  needs  to  take  at  a  single  meal  can  be 
thoroughly  masticated  in   fifteen   minutes,  why  is  it  better  to  spend 
a  longer  time  at  the  table  ? 

14.  What  is  meant  by  the  overlapping  of  meals  ?     What  bad  results 
follow  ?    How  avoided  ? 

PRACTICAL  WORK 

Examine  a  dissectible  model  of  the  human  abdomen  (Fig.  75),  noting 
the  form,  location,  and  connection  of  the  different  organs.  Find  the 
connection  of  the  esophagus  with  the  stomach,  of  the  stomach  with 
the  small  intestine,  and  of  the  small  intestine  with  the  large  intestine. 


ORGANS    AND    PROCESSES    OF   DIGESTION         169 

Sketch  a  general  outline  of  the  cavity,  and  locate  in  this  outline  its 
chief  organs. 

Where  it  is  desirable  to  learn  something  of  the  actual  structure  of  the 
digestive  organs,  the  dissection  of  the  abdomen  of  some  small  animal  is 
necessary.  On  account  of  unpleasant  features 
likely  to  be  associated  with  such  a  dissection, 
however,  this  work  is  not  recommended  for  im- 
mature pupils. 

Dissection  of  the  Abdomen.  (Optional)  — 
For  individual  study,  or  for  a  small  class,  a 
half-grown  cat  is  perhaps  the  best  available 
material.  It  should  be  killed  with  chloroform, 
and  then  stretched,  back  downward,  on  a  board, 
the  feet  being  secured  to  hold  it  in  place. 

The  teacher  should  make  a  preliminary  ex- 
amination of  the  abdomen  to  see  that  it  is  in  a        FIG.  75.  —  Model  for 
fit  condition  for  class  study.     If  the  bladder  is    demonstrating  the  abdo- 
un naturally    distended,    its    contents    may    be    men  and  its  contents, 
forced  out  by  slight  pressure.     The  following 

materials  will  be  needed  during  the  dissection,  and  should  be  kept  near 
at  hand  :  a  sharp  knife  with  a  good  point,  a  pair  of  heavy  scissors,  a 
vessel  of  water,  some  cotton  or  a  damp  sponge,  and  some  fine  cord. 
During  the  dissection  the  specimen  should  be  kept  as  clean  as  possible, 
and  any  escaping  blood  should  be  mopped  up  with  the  cotton  or  the 
sponge.  The  dissection  is  best  carried  out  by  observing  the  following 
order : 

1.  Cut  through  the  abdominal  wall  in  the  cente'r  of  the  triangular 
space  where  the  ribs  converge.     From  here  cut  a  slit  downward  to  the 
lower  portion  of  the  abdomen,  and   sideward   as    far   as    convenient. 
Tack  the  loosened  abdominal  walls  to  the  board,  and  proceed  to  study 
the  exposed  parts.     Observe  the  muscles  in  the  abdominal  walls,  and 
the  fold  of  the  peritoneum  which  forms  an  apron-like  covering  over  the 
intestines. 

2.  Observe  the  position  of  the  stomach,  liver,  spleen,  and  intestines, 
and  then,  by  pushing  the  intestines  to  one  side,  find  the  kidneys  and 
the  bladder. 

3.  Study  the  liver  with  reference  to  its   location,  size,   shape,  and 
color.     On  the  under  side,  find  the  gall  bladder,  from  which  a  small  tube 
leads  to  the  small  intestine.     Observe  the  portal  vein  as  it  passes  into 


I/O 


THE   VITAL   PROCESSES 


the  liver.     As  the  liver  is  filled  with  blood,  neither  it  nor  its  connecting 
blood  vessels  should  be  cut  at  this  time. 

4.  Trace  out  the  continuity  of  the  canal.     Find  the  esophagus  where 
it  penetrates  the  diaphragm  and  joins  the  stomach.     Find  next  the 
union  of  the  stomach  with  the  small  intestine.     Then,  by  carefully  fol- 
lowing the  coils  of  the  small  intestine,  discover  its  union  with  the  large 
intestine. 

5.  Within  the  first  coil  of  the  small  intestine,  as  it  leaves  the  stomach, 
find  the  pancreas.     Note  its  color,  size,  and  branches.     Find  its  con- 
nection with  the  small  intestine. 

6.  Beginning  at  the  cut  portion  of  the  abdominal  wall,  lift  the  thin 
lining  of  the  peritoneum  and  carefully  follow  it  toward  the  back  and 
central  portion  of  the  abdomen.      Observe  whether  it  extends  back 
of  or  in  front  of  the  kidneys,  the  aorta,  and  the  inferior  vena  cava. 
Find  where  it  leaves  the  wall  as  a  double  membrane,   the  mesentery, 
which  surrounds  and  holds  in  place  the  large  and  small  intestines. 
Sketch  a  coil  of  the  intestine,  showing  the  mesentery. 

7.  Find  in  the  center  of  the  -coils  of  small  intestine  a  long,  slender 
body  having  the  appearance  of  a  gland.     This  is  the  beginning  of  the 
thoracic  duct  and  is  called  the  receptacle  of  the  chyle.     From  this  the 
thoracic  duct  rapidly  narrows  until  it  forms  a  tiny  tube  difficult  to  trace 
in  a  small  animal. 

8.  Cut  away   about   two   inches   of  the  small   intestine   from   the 
remainder,  having  first  tied  the  tube  on  the  two  sides  of  the  section  re- 
moved.    Split  it  open  for  a  part  of  its  length,  and  wash  out  its  contents. 
Observe  its  coats.     Place  it  in  a  shallow  vessel  containing  water,  and 
examine  the  mucous  membrane  with  a  lens  to  find  the  villi.     Make  a 
drawing  of  this  section,  showing  the  coats. 

9.  Study  the  connection  of  the  small  intestine  with  the  large.     Split 
them  open  at  the  place  of  union,  wash  out  the  contents,  and  examine 
the  ileo-caecal  valve. 

10.  Observe  the  size,  shape,  and  position  of  the  kidneys.     Do  they 
lie  in  front  of  or  back  of  the  peritoneum  ?     Do  they  lie  exactly  opposite 
each  other  ?     Note  the  connection  of  each  kidney  with  the  aorta  and 
the  inferior  vena  cava  by  the  renal  artery  and  the  renal  vein.     Find  a 
slender  tube,  the  ureter,  running  from  each  kidney  to  the  bladder.     Do 
the  ureters  connect  with  the  top  or  with  the  base  of  the  bladder  ?    Show 
by  a  sketch  the  connection  of  the  kidneys  with  the  large  blood  vessels 
and  the  bladder. 


ORGANS    AND    PROCESSES    OF   DIGESTION          171 

To  demonstrate  the  Teeth.  —  Procure  from  the  dentist  a  collection  of 
different  kinds  of  teeth,  both  sound  and  decayed. 

(a)  Examine   external  surfaces  of  different  kinds  of  teeth,  notinf 

\      s  O 

general  shape,  cutting  or  grinding  surfaces,  etc.  Make  a  drawing  of  an 
incisor  and  also  of  a  molar. 

(£)  After  soaking  some  of  the  teeth  for  a  couple  of  days  in  warm 
water  saw  one  of  them  in  two  lengthwise,  and  another  in  two  crosswise, 
and  smooth  the  cut  surfaces  with  fine  emery  or  sand  paper.  Examine 
both  kinds  of  sections,  noting  arrangement  and  extent  of  dentine, 
enamel,  and  pulp.  Make  drawings. 

(c)  Examine  a  decayed  tooth.  Which  substance  of  the  tooth 
appears  to  decay  most  readily  ?  Why  is  it  necessary  to  cut  away  a  part 
of  the  tooth  before  filling  ? 

(<t)  Test  the  effect  of  acids  upon  the  teeth  by  leaving  a  tooth  over 
night  in  a  mixture  of  one  part  hydrochloric  acid  to  four  parts  water,  and 
by  leaving  a  second  tooth  for  a  couple  of  days  in  strong  vinegar. 
Examine  the  teeth  exposed  to  the  action  of  acids,  noting  results. 

To  show  the  Importance  of  Mastication.  —  Fill  two  tumblers  each 
half  full  of  water.  Into  one  put  a  lump  of  rock  salt.  Into  the  other 
place  an  equal  amount  of  salt  that  has  been  finely  pulverized.  Which 
dissolves  first  and  why  ? 

To  illustrate  Acid  and  Alkaline  Reactions.  —  To  a  tumbler  half 
full  of  water  add  a  teaspoonful  of  hydrochloric  or  other  acid,  as 
vinegar.  To  a  second  tumbler  half  full  of  water  add  an  equal  amount 
of  cooking  soda.  Taste  each  liquid,  noting  the  sour  taste  of  the  acid, 
and  the  alkaline  taste  of  the  soda.  Hold  a  piece  of  red  litmus  paper 
in  the  soda  solution,  noting  that  it  is  turned  blue.  Then  hold  a  piece 
of  blue  litmus  paper  in  the  acid  solution,  noting  that  it  is  turned 
red.  Add  acid  to  the  soda  solution,  and  soda  to  the  acid  solution, 
until  the  conditions  are  reversed,  testing  with  the  red  and  blue  litmus 
papers. 

Hold,  for  a  minute  or  longer,  a  narrow  strip  of  red  litmus  paper  in 
the  mouth,  noting  any  change  in  the  color  of  the  paper.  Repeat,  using 
blue  litmus  paper.  What  effect,  if  any,  has  the  saliva  upon  the  color  of 
the  papers  ?  Has  the  mouth  an  acid  or  an  alkaline  reaction  ? 

To  show  the  Action  of  Saliva  on  Starch.—  i  (Optional).  Prepare 
starch  paste  by  mixing  half  a  teaspoonful  of  starch  in  half  a  pint  of 
water  and  heating  the  mixture  to  boiling.  Place  some  of  this  in  a  test 
tube  and  thin  it  by  adding  more  water.  Then  add  a  small  drop  of 


1/2 


THE   VITAL   PROCESSES 


iodine  solution  (page  136)  to  the  solution  of  starch.  It  should  turn  a 
deep  blue  color.  This  is  the  test  for  starch. 

Now  collect  from  the  mouth,  in  a  clean  test  tube,  two  or  three  tea- 
spoonfuls  of  saliva.  Add  portions  of  this  to  small  amounts  of  fresh 
starch  solution  in  two  test  tubes.  Let  the  tubes  stand  for  five  or  ten 
minutes  surrounded  by  water  having  about  the  temperature  of  the  body. 
Test  for  changes  that  have  occurred  as  follows  : 

(a)  To  one  tube  add  a  little  of  the  iodine  solution.  If  it  does  not 
turn  blue,  it  shows  that  the  starch  has  been  converted  into  some  other 
substance  by  the  saliva.  (£)  To  the  other  tube  add  a  few  drops  of  a 
very  dilute  solution  of  copper  sulphate.  Then  add  sodium  (or  potassium) 
hydroxide,  a  few  drops  at  a  time,  until  the  precipitate  which  first  forms 
dissolves  and  turns  a  deep  blue.  Then  gradually  heat  the  upper 
portion  of  the  liquid  to  boiling.  If  it  turns  an  orange  or  yellowish  red 
color,  the  presence  of  a  form  of  sugar  (maltose  or  dextrose)  is  proved. 
See  page  136. 

2.  Hold  some  powdered  starch  in  the  mouth  until  it  completely  dis- 
solves and  observe  that  it  gradually  acquires  a  sweetish  taste.  This 
shows  the  change  of  starch  into  sugar. 

To  illustrate  the  Action  of  the  Gastric  Juice.  —  Add  to  a  tumbler 
two  thirds  full  of  water  as  much  scale  pepsin  (obtained  from  a  drug 
store)  as  will  stay  on  the  end  of  the  large  blade  of  a  penknife.  Then 
add  enough  hydrochloric  acid  to  give  a  slightly  sour  taste.  Place  in 
the  artificial  gastric  juice  thus  prepared  some  boiled  white  of  egg  which 
has  been  finely  divided  by  pressing  it  through  a  piece  of  wire  gauze. 
Also  drop  in  a  single  large  lump.  Keep  in  a  warm  place  (about  the 
temperature  of  the  body)  for  several  hours  or  a  day,  examining  from 
time  to  time.  What  is  the  general  effect  of  the  artificial  gastric  juice 
upon  the  egg? 

To  illustrate  Effect  of  Alcohol  upon  Gastric  Digestion.  —  Prepare  a 
tumbler  half  full  of  artificial  gastric  juice  as  in  the  above  experiment, 
and  add  10  cubic  centimeters  of  this  to  each  of  six  clean  test  tubes 
bearing  labels.  To  five  of  the  tubes  add  alcohol  from  a  burette  as 
follows:  (i)  .5  c.c.,  (2)  i  c.c.,  (3)  1.5  c.c.,  (4)  2  c.c.,  and  (5)  3  c.c., 
leaving  one  tube  without  alcohol.  Now  add  to  each  tube  about  {  gram 
of  finely  divided  white  of  egg  from  the  experiment  above,  and  place  all 
of  the  tubes  in  a  beaker  half  full  of  water.  Keep  the  water  a  little 
above  the  temperature  of  the  body  for  several  hours,  examining  the 
tubes  at  intervals  to  note  the  progress  of  digestion.  Inferences. 


CHAPTER   XI 
ABSORPTION,  STORAGE,  AND  ASSIMILATION 

THE  dissolved  nutrients,  to  reach  the  cells,  must  be  trans- 
ferred from  the  alimentary  canal  to  the  blood  stream. 
This  process  is  known  as  absorption.  In  general,  absorption 
means  the  penetration  of  a  liquid  into  the  pores  of  a  solid, 
and  takes  place  according  to  the  simple  laws  of  molecular 
movements.  The  absorption  of  food  is,  however,  not  a 
simple  process,  and  the  passage  takes  place  through  an 
active  (living)  membrane.  Another  difference  is  that  cer- 
tain foods  undergo  chemical  change  while  being  absorbed. 

Small  Intestine  as  an  Organ  of  Absorption.  —  While  ab- 
sorption may  occur  to  a  greater  or  less  extent  along  the 
entire  length  of  the  alimentary  canal,  most  of  it  takes 
place  at  the  small  intestine.  Its  "great  length,  its  small 
diameter,  and  its  numerous  blood  vessels  all  adapt  the 
small  intestine  to  the  work  of  absorption.  The  transverse 
folds  in  the  mucous  membrane,  by  retarding  the  food  in 
its  passage  and  by  increasing  the  absorbing  surface,  also 
aid  in  the  process.  But  of  greatest  importance  are  the 
minute  elevations  that  cover  the  surface  of  the  mucous 
membrane,  known  as 

The  Villi.  —  Each  single  elevation,  or.villus,  has  a  length 
of  about  one  fiftieth  of  an  inch  and  a  diameter  about  half 
as  great  (A,  Fig.  76),  and  contains  the  following  essential 
parts : 

i.  An  outer  layer  of  epithelial  cells,  resting  upon  a  con- 
nective tissue  support. 


r/4 


THE   VITAL   PROCESSES 


2.  A  small  lymph  tube,  called  a  lacteal,  which  occupies 
the  center  of  the  villus  and  connects  at  the  base  with  other 
lymph  tubes,  also  called  lacteals  (B,  Fig.  76). 

3.  A  network  of  capillaries. 

The  villi  are  structures  especially  adapted  to  the  work  of 
absorption,  and  they  are  found  only  in  the  small  intestine. 


FIG.  76. —  The  villi.  A.  Diagram  of  a  small  section  of  mucous  mem- 
brane of  small  intestine.  I.  Villi.  2.  Small  glands,  called  crypts. 

B.  Diagram  showing  structure  of  villi.  I.  Small  artery.  2.  Lacteal. 
3.  Villus  showing  termination  of  the  lacteal.  4.  Villus  showing  capillaries. 
5.  Villus  showing  both  the  lacteal  and  the  capillaries.  6.  Small  vein. 
7.  Layer  of  epithelial  cells. 

The  mucous  membrane  in  all  parts  of  the  canal,  however, 
is  capable  of  taking  up  some  of  the  digested  materials. 

Work  of  Capillaries  and  Lacteals.  —  The  capillaries  and 
lacteals  act  as  receivers  of  material  as  it  passes  through 
the  layer  of  epithelial  cells  covering  the  mucous  mem- 
brane. The  lacteals  take  up  the  digested  fats,1  and  the 
capillaries  receive  all  the  other  kinds  of  nutrients.  These 
vessels  do  not,  of  course,  retain  the  absorbed  materials, 
but  pass  them  on.  Their  final  destination  is  the  general 
circulation,  which  they  reach  by  two  well-defined  channels, 
or  routes. 

Routes  to  the  Circulation.  —  The  two  routes  from   the 

1  The  lacteals  (from  the  Latin  lacteus,  milky)  are  so  called  on  account  of  their 
appearance,  which  is  white,  or  milk-like,  due  to  the  fat  droplets. 


ABSORPTION,   STORAGE,  AND   ASSIMILATION       175 


place    of   absorption    to   the    general    circulation    are    as 
follows : 

1.  Route  taken  by  tJie  Fat.  —  The  fat  is  conveyed  by  the 
lacteals  from  the  villi  to  the  receptacle  of  the  chyle.     At 
this  place  it  mingles  with  the  lymph  from  the  lower  parts 
of  the  body,  and  with  it 

passes  through  the  tho- 
racic duct  to  the  left 
subclavian  vein.  Here 
it  enters  the  general 
circulation.  Thus,  to 
reach  the  general  circula- 
tion, the  fat  has  to  pass 
through  the  villi,  the 
lacteals,  the  receptacle 
of  the  chyle,  and  the 
thoracic  duct  (Fig.  77). 
Its  passage  through  these 
places,  like  the  move- 
ments in  all  lymph  ves- 
sels, is  slow,  and  it  is 
only  gradually  admitted 
to  the  blood  stream. 

2.  Route    of   All    the 
Nutrients    except    Fat.  — 
Water  and  salts  and  the 
digested  proteids  and  car- 
bohydrates, in  passing  into  the  capillaries,  mix  there  with 
the  blood.     But  this  blood,  instead  of  flowing  directly  to 
the  heart,  is  passed  through  the  portal  vein  to  the  liver, 
where  it  enters  a  second  set  of  capillaries  and  is  brought 
very  near  the  liver  cells.      From  the    liver  it  is   passed 
through  the  hepatic  veins  into  the  inferior  vena  cava,  and 


FIG.  77.  —  Diagram  of  routes 
food  canal  to  general  circulation, 
text. 


frv>m 
See 


I76  THE  VITAL   PROCESSES 

by  these  it  is  emptied  into  the  right  auricle.  This  route 
then  includes  the  capillaries  in  the  mucous  membrane  of  the 
stomach  and  intestines,  the  branches  of  the  portal  vein, 
the  portal  vein  proper,  the  liver,  and  the  hepatic  veins  (Fig. 
77).  In  passing  through  the  liver,  a  large  portion  of  the 
food  material  is  temporarily  retained  for  a  purpose  and  in  a 
manner  to  be  described  later  (page  177). 

Absorption  Changes.  —  During  digestion  the  insoluble 
foods  are  converted  into  certain  soluble  materials,  such  as 
peptones,  maltose,  and  glycerine, — the  conversion  being 
necessary  to  their  solution.  A  natural  supposition  is  that 
these  materials  enter  and  become  a  part  of  the  blood,  but 
examination  shows  them  to  be  absent  from  this  liquid. 
(See  Composition  of  the  Blood,  page  30.)  There  are  pres- 
ent in  the  blood,  however,  substances  closely  related  to  the 
peptones,  maltose,  glycerine,  etc. ;  substances  which  have 
in  fact  been  formed  from  them.  During  their  transfer 
from  the  food  canal,  the  dissolved  nutrients  undergo 
changes,  giving  rise  to  the  materials  in  the  blood.  Thus  are 
the  serum  albumin  and  serum  globulin  of  the  blood  derived 
from  the  peptones  and  proteoses ;  the  dextrose,  from  the 
maltose  and  other  forms  of  sugar ;  and  the  fat  droplets, 
from  the  glycerine,  fatty  acid,  and  soluble  soap. 

While  considerable  doubt  exists  as  to  the  cause  of  these 
changes  and  as  to  the  places  also  where  some  of  them 
occur,  their  purpose  is  quite  apparent.  The  materials 
forming  the  dissolved  foods,  although  adapted  to  absorp- 
tion, are  not  suited  to  the  needs  of  the  body,  and  if  intro- 
duced in  this  form  are  likely  to  interfere  with  its  work.1 
They  are  changed,  therefore,  into  the  forms  which  the 
body  can  use. 

1  Peptones  and  proteoses,  when  injected  directly  into  the  blood,  are  found  to  act 
as  poisons. 


ABSORPTION,   STORAGE,  AND   ASSIMILATION       177 

A  Second  Purpose  of  Digestion.  —  Comparing  the  digestive  changes 
with  those  of  absorption,  it  is  found  that  they  are  of  a  directly  opposite 
nature ;  that  while  digestion  is  a  process  of  tearing  down,  or  separating, 
—  one  which  reduces  the  food  to  a  more  finely  divided  condition  — 
there  is  in  absorption  a  process  of  building  up.  From  the  compara- 
tively simple  compounds  formed  by  digestion,  there  are  formed  during 
absorption  the  more  complex  compounds  of  the  blood.  The  one  excep- 
tion is  dextrose,  which  is  a  simple  sugar;  but  even  this  is  combined  in 
the  liver  and  the  muscles  to  form  the  more  complex  compound  known 
as  glycogen.  (See  Methods  of  Storage,  below.)  These  facts  have  sug- 
gested a  second  purpose  of  digestion  —  that  of  reducing  foods  to  forms 
sufficiently  simple  to  enable  the  body  to  construct  out  of  them  the  more 
complex  materials  that  it  needs.  Evidence  that  digestion  serves  such  a 
purpose  is  found  in  the  fact  that  both  proteids  and  carbohydrates  are 
reduced  to  a  simpler  form  than  is  necessary  for  dissolving  them.1 

The  Storage  of  Nutriment.  —  For  some  time  after  the 
taking  of  a  meal,  food  materials  are  being  absorbed  more 
rapidly  than  they  can  be  used  by  the  cells.  Following 
this  is  an  interval  when  the  body  is  taking  no  food,  but 
during  which  the  cells  must  be  supplied  with  nourishment. 
It  also  happens  that  the  total  amount  of  food  absorbed 
during  a  long  interval  may  be  in  excess  of  the  needs  of 
the  cells,  during  that  time;  and  it  is  always  possible,  as 
in  disease,  that  the  quantity  absorbed  is  not  equal  to  that 
consumed.  To  provide  against  emergencies,  and  to  keep 
up  a  uniform  supply  of  food  to  the  cells,  it  is  necessary 
that  the  body  store  up  nutrients  in  excess  of  its  needs. 

Methods  of  Storage.  — The  general  plan  of  storage 
varies  with  the  different  nutrients  as  follows : 

i.  The  carbohydrates  are  stored  in  the  form  of  glycogen. 
This,  as  already  stated  (page  120),  is  a  substance  closely 
resembling  starch.  It  is  stored  in  the  cells  of  both  the 

1  The  soluble  double  sugars  (maltose,  milk  sugar,  and  cane  sugar)  are  reduced 
to  the  simple  sugars  (dextrose  and  levulose).  Furthermore  the  action  on  the 
proteids  does  not  stop  with  the  production  of  peptones  and  proteoses,  but  these  in 
turn  are  still  further  reduced. 


I78 


THE   VITAL   PROCESSES 


FIG.  78.  —  Liver  cells  where 
is  stored  the  glycogen.  C.  Cap- 
illaries. 


liver  and  the  muscles,  but  mainly  in  the  liver  (Fig.  78).  It 
is  a  chief  function  of  the  liver  to  collect  the  excess  of  dex- 
trose from  the  blood  passing 
through  it,  and  to  convert  it 
into  glycogen,  which  it  then 
stores  within  its  cells.  It  does 
not,  however,  separate  all  of  the 
dextrose  from  the  blood,  a  small 
amount  being  left  for  supply- 
ing the  immediate  needs  of  the 
tissues.  As  this  is  used,  the 
glycogen  in  the  liver  is  changed 
back  to  dextrose  and,  dissolv- 
ing, again  finds  its  way  into  the 
blood.  In  this  way,  the  amount 

of  dextrose  in  the  blood  is  kept  practically  constant.  The 
carbohydrates  are  'stored  also  by  converting  them  into  fat. 

2.  The  fat  is  stored  for 
the  most  part  in  the  connect- 
ive tissue.  Certain  of  the 
connective  tissue  cells  have 
the  property  of  taking  fat 
from  the  blood  and  of  deposit- 
ing it  within  their  inclosing 
membranes  (Fig.  79).  When 
this  is  done  to  excess,  and 
the  cells  become  filled  with  FlG.  79.  _  stored-up  fat.  The 

fat,  they  form  the  SO-Called  figure  shows  four  connective  tissue 
adipose  tissue.  Most  of  this  cells  containing  small  particles  of  fat. 
.• r  j  j  ,,  I.  Nucleus.  2.  Protoplasm.  3.  Fat. 

tissue    is    found    under    the  ' 

4.  Connective  tissue  fibers. 

skin,  between   the   muscles, 

and  among  the  organs  occupying  the  abdominal  cavity. 

If   one   readily  takes  on  fat,    it   may    also  collect  in  the 


'.....a 


ABSORPTION,    STORAGE,  AND   ASSIMILATION       179 

connective  tissue  around  the  heart.  The  stored-up  fat  is 
redissolved  as  needed,  and  enters  the  blood,  where  it  again 
becomes  available  to  the  active  cells. 

3.  The  proteids  form  a  part  of  all  the  tissues,  and  for 
this  reason  are  stored  in  larger  quantities  than  any  of  the 
other  food  substances.  The  large  amount  of  proteid  found 
in  the  blood  may  also  be  looked  upon  as  storage  material. 
The  proteids  in  the  various  tissues  are  spoken  of  as  tissue 
proteids,  and  those  in  the  blood  as  circulating  proteids. 
The  proteids  of  the  tissues  serve  the  double  purpose  of 
forming  a  working  part  of  the  cell  protoplasm,  and  of  sup- 
plying reserve  food  material.  That  they  are  available  for 
supplying  energy,  and  are  properly  regarded  as  storage 
material,  is  shown  by  the  rapid  loss  of  proteid  in  starving 
animals.  When  the  proteids  are  eaten  in  excess  of  the 
body's  need  for  rebuilding  the  tissues,  they  are  supposed 
to  be  broken  up  in  such  a  manner  as  to  form  glycogen  and 
fat,  which  may  then  be  stored  in  ways  already  described. 

General  Facts  Relating  to  Storage. — The  form  into  which  the  food 
is  converted  for  storage  in  the  body  is  that  of  solids  —  the  form  that 
takes  up  the  least  amount  of  space.  These  solids  are  of  such  a  nature 
that  they  can  be  changed  back  into  their  former  condition  and,  by  dis- 
solving, reenter  the  blood. 

Only  energy-yielding  foods  are  stored.  Water  and  salts,  though  they 
may  be  absorbed  in  excess  of  the  needs  of  the  body,  are  not  converted 
into  other  substances  and  stored  away.  Oxygen,  as  already  stated  (page 
1 08),  is  not  stored.  The  interval  of  storage  may  be  long  or  short, 
depending  upon  the  needs  of  the  body.  In  the  consumption  of  stored 
material  the  glycogen  is  used  first,  then  as  a  rule  the  fat,  and  last  of 
all  the  proteids. 

Storage  in  the  Food  Canal.  —  Not  until  three  or  four 
hours  have  elapsed  are  all  the  nutrients,  eaten  at  a  single 
meal,  digested  and  passed  into  the  body  proper.  The  un- 
digested food  is  held  in  reserve,  awaiting  digestion,  and 


!8o  THE   VITAL   PROCESSES 

is  only  gradually  absorbed  as  this  process  takes  place. 
It  may  properly,  on  this  account,  be  regarded  as  stored 
material.  That  such  storage  is  of  advantage  is  shown  by 
the  observed  fact  that  substances  which  digest  quickly 
(sugar,  dextrin,  "predigested  foods,"  etc.)  do  not  supply 
the  needs  of  the  body  so  well  as  do  substances  which,  like 
starch  and  proteids,  digest  slowly.  Even  substances  digest- 
ing quite  slowly  (greasy  foods  and  pastry),  since  they  can 
be  stored  longer  in  the  food  canal,  may  be  of  real  ad- 
vantage where,  from  hard  work  or  exposure,  the  body 
requires  a  large  supply  of  energy  for  some  time.  These 
"  stay  by  "  the  laborer,  giving  him  strength  after  the  more 
easily  digested  foods  have  been  used  up.  Storage  by  the 
food  canal  is  limited  chiefly  to  the  stomach. 

Regulation  of  the  Food  Supply  to  the  Cells.  —  The 
storage  of  food  materials  is  made  to  serve  a  second  pur- 
pose in  the  plan  of  the  body  which  is  even  more  important 
than  that  of  supplying  nourishment  to  the  cells  during  the 
intervals  when  no  food  is  being  taken.  It  is  largely  the 
means  whereby  the  rate  of  supply  of  materials  to  the  cells 
is  regulated.  The  cells  obtain  their  materials  from  the 
lymph,  and  the  lymph  is  supplied  from  the  blood.  Should 
food  substances,  such  as  sugar,  increase  in  the  blood  beyond 
a  low  per  cent,  they  are  converted  into  a  form,  like  glyco- 
gen,  in  which  they  are  held  in  reserve,  or,  for  the  time 
being,  placed  beyond  the  reach  of  the  cells.  When, 
however,  the  supply  is  reduced,  the  stored-up  materials 
reenter  the  blood  and  again  become  available  to  the 
cells.  By  this  means  their  rate  of  supply  to  the  cells 
is  practically  constant. 

We  are  now  in  a  position  to  understand  why  carbohy- 
drates, fats,  and  proteids  are  so  well  adapted  to  the  needs 
of  the  body,  while  other  substances,  like  alcohol,  which 


ABSORPTION,   STORAGE,  AND   ASSIMILATION       181 

may  also  liberate  energy,  prove  injurious.  It  is  because 
foods  are  of  such  a  chemical  nature  that  they  are  adapted 
in  all  respects  to  the  body  plan  of  taking  up  and  using 
materials,  while  the  other  substances  are  lacking  in  some 
particular. 

Why  Alcohol  is  not  a  Food.  —  If  the  passage  of  alcohol 
through  the  body  is  followed,  it  is  seen,  in  the  first  place, 


B 


FIG.  80.  —  Diagrams  illustrating  the  relation  of  nutrients  and  the  non- 
relation  of  these  to  alcohol.  A.  Inter-relation  and  convertibility  of  proteids, 
fats,  and  carbohydrates  (after  Hall). 

B.  Diagram  showing  disposition  of  alcohol  if  this  substance  is  taken  in 
quantity  corresponding  to  that  of  the  nutrients  (F.  M.  W.).  The  alcohol 
thrown  off  as  waste  is  unoxidized  and  yields  no  energy. 

that  it  is  a  simple  liquid  and  undergoes  no  digestive  change  >, 
and  in  the  second  place,  that  it  is  rapidly  absorbed  from 
the  stomach  in  both  weak  and  concentrated  solutions. 
This  introduces  it  quickly  into  the  blood,  and  once  there, 
it  diffuses  rapidly  into  the  lymph  and  then  into  the  cells. 
Since  the  body  cannot  store  alcohol  or  convert  it  into  some 
nutrient  that  can  be  stored  (Fig.  80),  there  is  no  way  of 


lS2  THE   VITAL   PROCESSES 

regulating  the  amount  that  shall  be  present  in  the  blood,  ot 
of  supplying-  it  to  the  cells  as  their  needs  require.  They 
must  take  it  in  excess  of  their  needs,  regardless  of  the 
effect,  at  least  until  the  organs  of  excretion  can  throw  off 
the  surplus  as  waste.  Compared  with  proteid,  carbo- 
hydrates, or  fats,  alcohol  is  an  unmanageable  substance  in 
the  body.  Attempting  to  use  it  as  a  food  is  as  foolish  as 
trying  to  burn  gasolene  or  kerosene  in  an  ordinary  wood 
stove.  It  may  be  done  to  a  limited  extent,  but  is  an  ex- 
ceedingly hazardous  experiment.  Not  being  adapted  to 
the  body  method  of  using  materials,  alcohol  cannot  be 
classed  as  a  food. 

Assimilation.  —  Digestion,  absorption,  circulation,  and 
storage  of  foods  are  the  processes  that  finally  make  them 
available  to  the  cells  in  the  different  parts  of  the  "body. 
There  still  remains  another  process  for  these  materials  to 
undergo  before  they  serve  their  final  purposes.  This  last 
process,  known  as  assimilation,  is  the  appropriation  of 
the  food  material  by  the  cell  protoplasm.  In  a  sense  the 
storage  of  fat  by  connective  tissue  cells  and  of  glycogen  by 
the  liver  cells  is  assimilation.  The  term  is  limited,  how- 
ever, to  the  disposition  of  material  with  reference  to  its 
final  use.  Whether  all  the  materials  used  by  the  cells 
actually  become  a  part  of  the  protoplasm  is  not  known. 
It  is  known,  however,  that  the  cells  are  the  places  where 
most  of  the  oxidations  of  the  body  occur  and  that  materials 
taking  part  in  these  oxidations  must,  at  least,  come  in 
close  contact  with  the  protoplasm.  Assimilation,  then,  is 
the  last  event  in  a  series  of  processes  by  which  oxygen, 
food  materials,  and  cell  protoplasm  are  brought  into  close 
and  active  relations.  The  steps  leading  up  to  assimilation 
are  shown  in  Table  II. 


ABSORPTION,   STORAGE,  AND   ASSIMILATION       183 


'Q 

0) 

i 

n  u  t-,  in 

o  *>  o>  .a 

o  o  c  u 

td 

0 

c 

g 

^'S"^ 

**  "C  «.  ~ 

H 

'2o 

•sj 

s  . 

c 

*s°° 

--  w  £  e 
~5  c  x  .5 

z  o 

•81 

en  oj 

V 

2       X!  C 

c 

'•:£  ° 

§3 

•5  o 

^  ?i 

o 

fe  rt         3 

o 

-2  ~  c    • 

PSQ 

o  — 

>>2 

^ 

en  =  -S  T3' 

3 

o*"^.2  c 

Q 
Z 

t.  rt 

ovc 

0)  _ 

•a  S 

5  £  ^   C   § 

O 

1  E  §5  "> 

a 

<2 

5° 

o 

^SJ-oSS 

C 

2Jc  cA  8  "p. 

'o'o 

a  A 

g°£ 

r^  bjO 

r  S 

0) 

II 

.S  c 

Id 

o>  > 

o  "^  c  «; 

O 

&~—  jn 

f  '^ 

^ 

T3 

H 
1 

rt)   ^ 

O  (u  ~ 

•*-  o 

C  c 
""  C 

i/i'o  in 

As  glycogei 
by  the  live 
some  exi 
muscle  ce 

Is  not  store 
sense  that 
foods  are. 

Not  stored. 

Is  not  store 

J 

1  |J.s 

O  X  O  _J 

c2 

^ 

C   S   a! 

13 

ROUTE  TO  THE  GENERA 
CIRCULATION 

—  ""    U.C 
u   C  *"  2  * 

3  J3   01    o   o 

Through  the  lacteals 
the  thoracic  duct,  1 
which  it  is  emptied  in 
the  left  subclavian  vei 

Through  the  portal  vei 
liver,  hepatic  veins,  in 
inferior  vena  cava. 

1    . 
£  S 

X)    0> 

-•£ 
|"S 

By  way  of  the  portal  vei 
liver,  and  hepatic  vei 
into  inferior  vena  cav 

Already  in  the  gener 
circulation. 

i    in  o)  1) 

o>  D  o)  o  <n 

in 

QJ      1      U     1) 

D  ~  •- 

, 

D.  0>    OXJ-S 

1 

s  s  §:: 

<u  o;J  0 
J3  O  U  « 
•*-•  i-i       'O 

oO.S-s 

*"S!§S  0. 

_    0    O    "    O 

2  X<n  rt^ 

.S  "Hb_«  >>__ 

u 

j3 
'S. 

||«* 

~   °   S 

;|i 

D, 

n    . 

!ft 

~.2 

1 

•S^§2 
to-"  a0- 

C      -  <u    0) 

•|  a  o.^^ 

aS-gSj 
ss  rt.S  jo 

HH 

H  "  S  '"S  'a' 

M£X««    u    0 

.S     •"  -a  o)  5 
I8J2  *  §£-° 

cS  nl  «  TO        0) 

O.o;£  &£•£ 
OS  5  i-  , 
c^.§  S^o 

Enters  the  ca] 
dextrose. 

o,        "  .H 
^  ^Sl 

IP  si 

rt  ™  ^  b£  o 

h 

Taken  up 
capillaries 
undergoing 
change. 

Taken  up  by 
laries  at  the 

6ig-g.- 

^oTg-d 

v  c  S3  « 

S.8.ISJ 

•S'C  g  rt  o 

S.O)  S  i3 

o 

0 

0 

2  T-!            C  '^ 

O    O    D  ^  -2» 

*  MX 

c 

C 

.£  c  £  «.o 

c  ^-'5  13  o 

2  ^  ^  ^ 

E 

•^    D/J  ^         *^ 

,,  t   ^ 

S 

V     , 

H 

*o      ^  ^o  ^ 

*^      "o  u  «i 

•d  u  o  « 

O    0) 

8 

&  W       flj  K 

U          t/i  ^    id 

u  ^ 

M  M 

tx  tuo 

O 

C   w   ^'S    c 

C  2  TJ  •        C 

3  "  £—     • 

S  c 

T-!     ^ 

IJ 

^  *o  c  >.  rt 

C^ 

•^  -2-  2  o  & 

-C  ni  rt  J3  p* 

o;  o>2  e  u 

o 

^ 

u 

K 

1:3 

5 

c 

3 

m 

o 

T3 

^ 

L> 

E~ 

• 

• 

'o! 

u 

0) 

c  rt 
C  <n 

M 

0 

•*-• 

B 

rt 

O 

&* 

1 

£ 

£ 

* 

U 

0 

X84  THE   VITAL   PROCESSES 

Tissue  Enzymes.  —  The  important  part  played  by  enzymes  in  the 
digestion  of  the  food  has  suggested  other  uses  for  them  in  the  body. 
It  has  been  recently  shown  that. many  of  the  chemical  changes  in  the 
tissues  are  in  all  probability  due  to  the  presence  of  enzymes.  An  illus- 
tration of  what  a  tissue  enzyme  may  do  is  seen  in  the  changes  which 
fat  undergoes.  In  order  for  the  body  to  use  up  its  reserve  fat,  it  must 
be  transferred  from  the  connective  tissue  cells,  where  it  is  stored,  to  the 
cells  of  the  active  tissues  where  it  is  to  be  used.  This  requires  that  it 
be  reduced  to  the  form  of  a  solution  and  that  it  reenter  the  blood.  In 
other  words,  it  must  be  redigested.  For  bringing  about  these  changes 
a  substance  identical  in  function  with  the  steapsin  of  the  pancreatic 
juice  has  been  shown  to  exist  in  several  of  the  tissues. 

Although  this  subject  is  still  under  investigation,  it  may  be  stated 
with  certainty  that  there  are  present  in  the  tissues,  enzymes  that  change 
dextrose  to  glycogen  and  vice  versa,  that  break  down  and  build  up  the 
proteids,  and  that  aid  in  the  oxidations  at  the  cells.  The  necessity 
for  such  enzymes  is  quite  apparent. 

Summary.  — The  digested  nutrients  are  taken  up  by  the 
capillaries  and  the  lymph  vessels  and  transferred  by  two 
routes  to  the  circulation.  In  passing  from  the  alimentary 
canal  into  the  circulation  the  more  important  of  the  foods 
undergo  changes  which  adapt  them  to  the  needs  of  the 
body.  Since  materials  are  absorbed  more  rapidly  than 
they  are  used,  means  are  provided  for  storing  them  and 
for  supplying  them  to  the  cells  as  their  needs  require. 
Capability  of  storage  is  an  essential  quality  of  energy- 
yielding  foods ;  and  substances,  such  as  alcohol,  which  lack 
this  quality  are  not  adapted  to  the  needs  of  the  body.  For 
causing  the  chemical  changes  that  occur  in  the  storage  of 
foods,  as  well  as  the  oxidations  at  the  cells,  the  presence 
of  active  agents,  or  enzymes,  is  necessary. 

Exercises. —  i.  In  what  respects  does  the  absorption  of  food 
materials  from  the  alimentary  canal  differ  from  the  absorption  of  a 
simple  liquid  by  a  solid? 


ABSORPTION,    STORAGE,  AND    ASSIMILATION       185 

2.  In  what  different  ways  is  the  small  intestine  especially  adapted 
to  the  work  of  absorption  ? 

3.  What  are  the  parts  of  a  villus?     What  are  the  lacteals?     Ac- 
count for  the  name. 

4.  What  part  is  played  by  the  capillaries  and  the  lacteals  in  the 
work  of  absorption  ?     How  does  their  work  differ? 

5.  What  changes,  if  any,  take  place  in  water,  common  salt,  fat, 
proteids,  and  carbohydrates  during  absorption  ? 

6.  What  double  purpose  is  served  by  the  processes  of  digestion? 

7.  Trace  the  passage  of  proteids,  fats,  and  carbohydrates  from  the 
small  intestine  into  the  general  circulation. 

8.  What  is  the  necessity  for  storing  nutrients  in  the  body?     Why 
is  it  not  also  necessary  to  store  up  oxygen  ? 

9.  In   what   form   and   at    what   places   is   each   of  the  principal 
nutrients  stored  ? 

10.  How  is  the  rate  of  supply  of  food  to  the  cells  regulated?  Why 
is  the  body  unable  to  regulate  the  supply  of  alcohol  to  the  cells  when 
this  substance  is  taken  ? 

it.  Explain  Fig.  80,  page  181.  What  becomes  of  the  alcohol  if 
this  is  taken  in  any  but  very  small  quantities  ? 

12.  State  the  general  purpose  of  enzymes  in  the  body.  Name  the 
enzymes  found  in  each  of  the  digestive  fluids.  What  ones  are  found 
in  the  tissues  ? 

PRACTICAL  WORK 

Illustrate  the  ordinary  meaning  of  the  term  "  absorption  "  by  bringing 
the  end  of  a  piece  of  crayon  in  contact  with  water,  or  a  piece  of  blotting 
paper  in  contact  with  ink,  noting  the  passage  of  the  liquid  into  the 
crayon  or  the  paper.  Show  how  absorption  from  the  food  canal  differs 
from  this  kind  of  absorption. 

Show  by  a  diagram  similar  to  Fig.  77  the  two  routes  by  which  the 
foods  pass  from  the  alimentary  canal  into  the  blood  stream. 


CHAPTER   XII 
ENERGY  SUPPLY  OF  THE  BODY 

IF  one  stops  taking  food,  it  becomes  difficult  after  a  time 
for  him  to  move  about  and  to  keep  warm.  These  results 
show  that  food  has  some  relation  to  the  energy  of  the  body, 
for  motion  and  heat  are  forms  of  energy.  The  relation  of 
oxygen  to  the  supply  of  energy  has  already  been  discussed 
(Chapter  VIII).  We  are  now  to  inquire  more  fully  into 
the  energy  supply  of  the  body,  and  to  consider  those  condi- 
tions which  make  necessary  the  introduction  of  both  food 
and  oxygen  for  this  purpose. 

Kinds  of  Bodily  Energy.  —  The  healthy  body  has  at  any 
time  a  considerable  amount  of  potential,  or  reserve,  energy, 
—  energy  which  it  is  not  using  at  the  time,  but  which  it  is 
able  to  use  as  its  needs  require.  When  put  to  use,  this 
energy  is  converted  into  such  forms  of  kinetic  energy 1  as 
are  indicated  by  the  different  kinds  of  bodily  power.  These 
are  as  follows : 

I.  Power  of  Motion. — The  body  can  move  itself  from 
place  to  place  and  it  can  give  motion  to  things  about  it. 

1  Energy,  which  is  defined  as  the  ability  to  do  work,  or  to  cause  motion,  exists  in 
two  general  types,  or  forms,  known  as  kinetic  energy  and  as  potential  energy. 
Kinetic  energy  is  energy  at  work,  or  energy  in  the  act  of  producing  motion  ;  while 
potential  energy  is  reserve,  or  stored,  energy.  All  moving  bodies  have  kinetic 
energy,  and  all  stationary  bodies  which  have  within  them  the  capability  of  causing 
motion  possess  potential  energy.  A  bent  bow,  a  piece  of  stretched  rubber,  a  sus- 
pended weight,  the  water  above  a  mill  dam,  all  have  the  capability  of  causing 
motion  and  all  have  potential  energy.  Examples  of  kinetic  energy  are  found  in 
the  movements  of  machinery,  in  steam  and  electricity,  in  winds,  and  in  currents  of 
water.  Kinetic  is  the  active,  and  potential  the  inactive,  form  of  energy. 

186 


ENERGY    SUPPLY   OF   THE   BODY 


I87 


2.  Heat  Power.  —  The  body  keeps  itself  warm  and  is 
able  to  communicate  warmth  to  its  surroundings. 

3.  Nervous  Power.  —  Through  the  nervous  system  the 
body  exercises  the  power  of  control  over  its  different  parts. 

As  motion,  heat,  and  nervous  power  the  body  uses  most 
of  its  energy. 

The  Source  of  Bodily  Energy.  —  As  already  indicated, 
the  energy  of  the  body  is  supplied  through  the  food  and 
the  oxygen.  These  contain  energy  in  the  potential  form, 
which  becomes  kinetic  (active)  through  their  uniting  with 
each  other  in  the  body.  Somewhat  as  the  power  of  the 
steam  engine  is  derived  from  the  combustion  of  fuel  in 
the  furnaces,  the  energy  of  the  body  is  supplied  through 
the  oxidations  at  the  cells.  How  the  food  and  oxygen 
come  to  possess  energy  is  seen  by  a  study  of  the  general 
methods  by  which  energy  is-stored  up  and  used. 

Simple  Methods  of  Storing  Energy.  —  Energy  is  stored 
by  converting  the  kinetic 
into  the  potential  form. 
Two  of  the  simplest  ways 
of  doing  this  are  the  fol- 
lowing: 

i.  Storing  of  Energy 
through  Gravity.  —  On  ac- 
count of  the  attraction  be- 
tween the  earth  and  all 
bodies  upon  the  earth,  the 
mere  lifting  of  a  weight  puts 
it  in  a  position  where  gravity 
can  cause  it  to  move  (Fig. 
81).  As  a  consequence  the 

raising  of  bodies  above  the  earths  surface  is  a  means  of 
storing  energy  —  the    energy   remaining    stored    until   the 


FIG.  81.  —  Simple  device  for  stor- 
ing energy  through  gravity. 


1 88  THE   VITAL  PROCESSES 

bodies  fall.  As  they  fall,  the  stored-up  (potential)  energy 
becomes  kinetic  and  can  be  made  to  do  work. 

2.  Storing  of  Energy  through  Elasticity.  —  Energy  is 
stored  also  by  doing  work  in  opposition  to  elasticity,  as  in 
bending  a  bow  or  in  winding  a  clock  spring.  The  bending, 
twisting,  stretching,  or  compressing  of  elastic  substances 
puts  them  in  a  condition  of  strain  which  causes  them  to 
exert  a  pressure  (called  elastic  force)  that  tends  to  restore 
them  to  their  former  condition.  Energy  stored  by  this 
means  becomes  active  as  the  distorted  or  compressed  sub- 
stance returns  to  its  former  shape  or  volume. 

These  simple  methods  of  storing  energy  will  serve  to 
illustrate  the  general  principles  upon  which  such  storage 
depends: 

1.  To  store  energy,  energy  must  be  expended,  or  work 
done. 

2.  The  work  must  be  against  some  force,  such  as  gravity 
or  elasticity,  which  can  undo  the  work,  i.e.,  bring  about  an 
effect  opposite  to  that  of  the  work. 

3.  The  stored  energy  becomes   active  (kinetic)  as  the 
force  through  which  the  energy  was  stored  undoes  the 
work,  or  puts  the  substance  upon  which  the  work  was 
done  into  its  former  condition  (gravity  causing  bodies  to 
fall,  etc.). 

These  principles  are  further  illustrated  by  the 
Storing  of  Energy  through  Chemical  Means.  —  A  good 
example  of  storing  energy  by  chemical  means  is  that  of 
decomposing  water  with  electricity.  If  a  current  of  elec- 
tricity is  passed  through  acidulated  water  in  a  suitable 
apparatus  (Fig.  82),  the  water  separates  into  its  component 
gases,  oxygen  and  hydrogen.  These  gases  now  have 
power  (energy)  which  they  did  not  possess  before  they 
were  separated.  The  hydrogen  will  burn  in  the  oxygen, 


ENERGY   SUPPLY   OF   THE   BODY 


189 


giving  heat;  and  if  the  two  gases  are  mixed  in  the  right 
proportions  and  then  ignited,  they  explode  with  violence. 
This  energy  was  derived  from  the  elec- 
tricity. It  was  stored  by  decomposing 
the  water. 

Energy  is  stored  by  chemical  means 
by  causing  it  to  do  work  in  opposition 
to  the  force  of  chemism,  or  chemical 
affinity.  Instead  of  changing  the  form 
of  bodies  or  moving  them  against 
gravity,  it  overcomes  the  force  that 
causes  atoms  to  unite  and  to  hold 
together  after  they  have  united.  Since 
in  most  cases  the  atoms  on  separating 
from  any  given  combination  unite  at 
once  to  form  other  combinations,  we 
may  say  that  energy  is  stored  wJien 
strong  chemical  combinations  are  broken 
^lp  and  weak  ones  formed.  Energy  decomposing  water  with 
stored  by  this  means  becomes  active 
when  the  atoms  of  weak  combinations  unite  to  form  com- 
binations that  are  strong.1 

How  Plants  store  the  Sun's  Energy.  —  The  earth's  sup- 
ply of  energy  comes  from  the  sun.  While  much  of  this, 
after  warming  and  lighting  the  earth's  surface,  is  lost  by 
radiation,  a  portion  of  it  is  stored  up  and  retained.  The 
sun's  energy  is  stored  both  through  the  force  of  gravity 2 

1  As  the  atoms  of  hydrogen  and  oxygen  that  make  up  the  molecules  of  water 
separate,  they  unite  with  atoms  of  their  own  kind  — the  hydrogen  with  hydrogen 
and  the  oxygen  with  oxygen  atoms.     Since  these  combinations  are  weaker  than 
those  of  the  water  molecules,  energy  is  required  to  bring  about  the  change.     But 
when  hydrogen  burns  in  the  oxygen,  the  change  is  from  a  weaker  to  a  stronger  com- 
bination.    The  stored-up  energy  is  then  given  up  or  becomes  active. 

2  In  the  evaporation  of  water,  the  energy  of  the  sun  is  stored  with  reference  to 
the  force  of  gravity.     In  evaporating,  w.iter  rises  as  a  gas,  or  vapor,  above  the  earth's 


FIG. 
energy 
means. 


82.  —  Storing 
by    chemical 

Apparatus    for 


190 


THE    VITAL   PROCESSES 


and  by  chemical  means,  the  latter  being  the  more  impor 
tant  of  the  two  methods.  Plants  supply  the  means  for 
storing  it  chemically  (Fig.  83).  Attention  has  already  been 
called  to  the  fact  (page  112)  that  growing  plants  are  con- 
tinually taking  carbon  dioxide 
into  their  leaves  from  the  air. 
This  they  decompose,  adding 
the  carbon  to  compounds  in 
their  tissues  and  returning 
the  oxygen  to  the  air.  It  is 
found,  however,  that  this  pro- 
cess does  not  occur  unless  the 
plants  are  exposed  to  sunlight. 
The  sunlight  supplies  the 
energy  for  overcoming  the  at- 
traction between  the  atoms  of 
oxygen  and  the  atoms  of  car- 
bon, while  the  plant  itself 
serves  as  the  instrument 
through  which  the  sunlight 
acts.  The  energy  for  decomposing  the  carbon  dioxide 
then  comes  from  the  sun,  and  through  the  decomposition 
of  the  carbon  dioxide  the  sun's  energy  is  stored  —  becomes 
potential.  It  remains  stored  until  the  carbon  of  the  plant 
again  unites  with  the  oxygen  of  the  air,  as  in  combustion. 

The  Sun's  Energy  in  Food  and  Oxygen.  —  Food  is  derived 
directly  or  indirectly  from  plants  and  sustains  the  same 
relation  -to  the  oxygen  of  the  air  as  do  the  plants  them- 
selves. (The  elements  in  the  food  have  an  attraction  for 

surface,  but  on  condensing  into  a  liquid,  it  falls  as  rain.  It  then  finds  its  way  through 
streams  back  to  the  ocean.  All  water  above  the  sea  level  is  in  such  a  position  that 
gravity  can  act  on  it  to  cause  motion,  and  it  possesses,  on  this  account,  potential  or 
siored-up  energy.  It  is  because  of  this  energy  that  rapids  and  waterfalls  are  such 
important  sources  of  power. 


FIG.  83.  —  Nature's  device  for 
storing  energy  from  the  sun.  See 
text. 


ENERGY    SUPPLY   OF    THE    BODY 


IQI 


the  oxygen,  but  are  separated  chemically  from  it.)  On 
account  of  this  relation  they  have  potential  energy  —  the 
energy  derived  through  the  plant  from  the  sun.  When  a 
person  eats  the  food  and  breathes  the  oxygen,  this  energy 
becomes  the  possession  of  the  body.  It  is  then  converted 
into  kinetic  energy  as  the  needs  of  the  body  require. 

From  the  Sun  to  the  Cells.  —  It  thus  appears  that  the 
body  comes  into  possession  of  energy,  and  is  able  to  use 
it,  through  a  series  of  transferences  and  transformations 
that  can  be  traced  back  to  the  sun.1  Coming  to  the  earth 
as  kinetic  energy,  it  is  transformed  into  potential  energy 
and  stored  in  the  compounds  of  plants  and  in  the  oxygen 
of  the  air.  Through  the  food  and  the  oxygen  the  poten- 
tial energy  is  transferred  to  the  cells  of  the  body.  Then 
by  the  uniting  of  the  food  and  the  oxygen  at  the  cells 
(oxidation),  the  potential  becomes  kinetic  energy  and  is 


1  Energy,  like  matter,  can  neither  be  created  nor  destroyed, 
ever,  be  transferred  from  one  body  to  another  and 
transformed  from  one  form  to  another  form.  When- 
ever work  is  done,  energy  is  transferred  from  the  body 
doing  the  work,  to  the  body  upon  which  the  work  is 
done.  During  this  process  there  may,  or  may  not,  be 
a  transformation  of  energy.  In  turning  a  grindstone, 
kinetic  energy  is  passed  to  the  stone  and  used  without 
transformation,  but  in  winding  a  clock,  the  kinetic  energy 
from  the  hand  is  transformed  into  potential  energy  in 
the  clock  spring.  Then  as  the  clock  runs  down  this  is 
retransformed  into  kinetic  energy,  causing  the  movements 
of  the  wheels. 

Not  only  is  kinetic  transformed  into  potential  energy 
and  vice  versa,  but  the  different  forms  of  kinetic  energy 
(heat,  light,  electricity,  sound,  and  mechanical  motion) 
are  readily  transformed  the  one  into  the  other.  With 
suitable  devices,  mechanical  motion  can  be  changed  into 
heat,  sound,  or  electricity;  heat  into  motion  and  light; 
and  electricity  into  all  the  other  forms  of  energy.  These 


It  can,  how- 


FIG.  84.  —  Simple 
apparatus  for  illus- 
trating transformation 


of    energy.     Potential 

transformations  are  readily  explained  by  the' fact  that  energy  is  converted 
the  different  varieties  of  kinetic  energy  are  but  different  into  heal  antl  heat 
forms  of  motion  (Fig.  84).  into  motion. 


192  THE   VITAL  PROCESSES 

used  by  the  body  in  doing  its  work.  The  phrase  "  Child 
of  the  Sun  "  has  sometimes  been  applied  to  man  to  express 
his  dependence  upon  the  sun  for  his  supply  of  energy. 

Why  Oxygen  and  Food  are  Both  Necessary.  —  The  neces- 
sity for  introducing  both  oxygen  and  food  into  the  body 
for  the  purpose  of  supplying  energy  is  now  apparent. 
The  energy  which  is  used  in  the  body  is  not  the  energy 
of  food  alone.  Nor  is  it  the  energy  of  oxygen  alone. 
It  belongs  to  both.  It  is  due  to  their  attraction  for  each 
other  and  their  condition  of  separation.  It  cannot,  there- 
fore, become  kinetic  except  through  their  union.  To  intro- 
duce one  of  these  substances  into  the  body  without  the  other, 
would  neither  introduce  the  energy  nor  set  it  free.  They 
must  both  be  introduced  into  the  body  and  there  caused  to 
unite. 

Bodily  Control  of  Energy.  —  A  fact  of  importance  in  the 
supply  of  energy  to  the  body  is  that  the  rate  of  transfor- 
mation (changing  of  potential  to  kinetic)  is  just  sufficient 
for  its  needs.  It  is  easily  seen  that  too  rapid  or  too  slow 
a  rate  would  prove  injurious.  The  oxidations  at  the  cells 
are,  therefore,  under  such  control  that  the  quantity  of 
kinetic  energy  supplied  to  the  body  as  a  whole,  and  to 
the  different  organs,  is  proportional  to  the  work  that  is 
done.  This  is  attained,  in  part  at  least,  through  the  ability 
of  the  body  to  store  up  the  food  materials  and  hold  them 
in  reserve  until  they  are  to  be  oxidized  (page  180). 

Animal  Heat  and  Motion.  —  Most  of  the  body's  energy 
is  expended  as  heat  in  keeping  warm.  It  is  estimated  that 
as  much  as  five  sixths  of  the  whole  amount  is  used  in  this 
way.  The  proportion,  however,  varies  with  different 
persons  and  is  not  constant  in  the  same  individual  during 
different  seasons  of  the  year.  This  heat  is  used  in  keeping 
the  body  at  that  temperature  which  is  best  suited  to  carry- 


ENERGY   SUPPLY   OF   THE   BODY  193 

ing  on  the  vital  processes.  All  parts  of  the  body,  through 
oxidation,  furnish  heat.  Active  organs,  however,  such  as 
the  muscles,  the  brain,  and  the  glands  (especially  the  liver), 
furnish  the  larger  share.  The  blood  in  its  circulation  serves 
as  a  heat  distributer  for  the  body  and  keeps  the  tempera- 
ture about  the  same  in  all  its  parts  (page  33). 

Next  to  the  production  of  heat,  in  the  consumption  of 
the  body's  energy,  is  the  production  of  motion.  This 
topic  will  be  considered  in  the  study  of  the  muscular 
system  (Chapter  XV). 

Some  Questions  of  Hygiene.  —  The  heat-producing  ca- 
pacity of  the  body  sustains  a  very  important  relation  to 
the  general  health.  A  sudden  chill  may  result  in  a  num- 
ber of  derangements  and  is  supposed  to  be  a  predisposing 
cause  of  colds.  One's  capacity  for  producing  heat  may  be 
so  low  that  he  is  unable  to  respond  to  a  sudden  demand 
for  heat,  as  in  going  from  a  warm  room  into  a  cold  one. 
As  a  consequence,  the  body  is  unable  to  protect  itself 
against  unavoidable  exposures. 

Impairment  of  tJie  lieat-producing  capacity  is  brought 
about  in  many  ways.  Several  diseases  do  this  directly,  or 
indirectly,  to  quite  an  extent.  In  health  too  great  care  in 
protecting  the  body  from  cold  is  the  most  potent  cause  of 
its  impairment.  Staying  in  rooms  heated  above  a  tem- 
perature of  70°  F.,  wearing  clothing  unnecessarily  heavy, 
and  sleeping  under  an  excess  of  bed  clothes,  all  diminish 
the  power  of  the  body  to  produce  heat.  They  accustom 
it  to  producing  only  a  small  amount,  so  that  it  does  not 
receive  sufficient  of  what  might  be  called  heat-producing 
exercise.  Lack  of  physical  exercise  in  the  open  air,  as 
well  as  too  much  time  spent  in  poorly  lighted  and  ven- 
tilated rooms,  tends  also  to  reduce  one's  ability  to  produce 
heat.  Moreover,  since  most  of  the  heat  of  the  body  comes 


194 


THE   VITAL   PROCESSES 


from  the  union  of  oxygen  and  food  materials  at  the  cells, 
a  lack  of  either  of  these  will  interfere  with  the  production 
of  heat. 

Results  of  Exhaustion.  —  Through  overwork,  or  excesses 
in  pleasurable  pursuits,  one  may  make  greater  demands 
upon  the  energy  of  his  body  than  it  can  properly  supply. 
The  resulting  condition,  known  as  exhaustion,  is  not  only 
a  matter  of  temporary  inconvenience,  but  may  through 
repetition  lead  to  a  serious  impairment  of  the  health.  It 
should  be  noted,  in  this  connection,  that  the  energy  of  the 
body  is  spent  in  two  general  ways  :  first,  in  carrying  on  the 
vital  processes  ;  and  second,  in  the  performance  of  vol- 
untary activities.  Since,  in  all  cases,  there  is  a  limit  to 
one's  energy,  it  is  easily  possible  to  expend  so  much  in  the 
voluntary  activities  that  the  amount  left  is  not  sufficient  for 
the  vital  processes.  This  leads  to  various  disturbances  and, 
among  other  things,  renders  the  body  less  able  to  supply 
itself  with  energy. 

The  Problem  of  Increasing  One's  Energy.  —  Since  the 
energy  supply  is  kept  up  through  the  food  and  the  oxygen, 
it  might  be  inferred  that  the  introduction  of  these  sub- 
stances into  the  body  in  larger  amounts  would  increase  the 
energy  at  one's  disposal.  This  does  not  necessarily  follow. 
Oxidation  at  the  cells  is  preceded  by  digestion,  absorption, 
circulation,  and  assimilation.  It  is  followed  and  influenced 
by  the  removal  of  wastes  from  the  body.  A  careful  study 
of  the  problem  leads  to  the  conclusion  that  while  the 
energy  supply  to  the  body  does  depend  upon  the  intro- 
duction of  the  proper  amounts  of  food  and  oxygen,  it  also 
depends  upon  the  efficiency  of  the  vital  processes.  The 
maximum  amount  of  energy  may,  therefore,  be  expected 
when  the  body  is  in  a  condition  of  perfect  health.  Hence, 
one  desiring  to  increase  the  amount  of  his  energy  must 


ENERGY    SUPPLY    OF   THE    BODY  195 

give  attention   to  all   those  conditions  that   improve  the 
health. 

Effect  of  Stimulants  on  the  Energy  Supply.  —  In  the  effort  to  get  out 
of  the  body  as  much  as  possible  of  work  or  of  pleasure,  various  stimu- 
lants, such  as  alcohol,  tobacco,  and  strong  tea  and  coffee,  have  been 
used.  Though  these  have  the  effect  of  giving  a  temporary  feeling  of 
strength  and  of  enabling  the  individual  in  some  instances  to  accomplish 
results  which  he  could  not  otherwise  have  brought  about,  the  general 
effect  of  their  use  is  to  lessen,  rather  than  to  increase,  the  sum  total  of 
bodily  power.  The  student,  for  example,  who  drinks  strong  coffee  in 
order  to  study  late  at  night  is  able  to  command  less  energy  on  the  day 
following.  While  enabling  him  to  draw  upon  his  reserve  of  nervous 
power  for  the  time  being,  the  coffee  deprives  him  of  sleep  and  needed 
rest. 

The  danger  of  stimulants,  so  far  as  energy  is  concerned,  is  this : 
they  tend  to  exhaust  the  bodily  reserve  so  that  there  is  not  sufficient 
left  for  properly  running  the  vital  processes.  Evidences  of  their  weak- 
ening effect  are  found  in  the  feeling  of  discomfort  and  lassitude  which 
result  when  stimulants  to  which  the  body  has  become  accustomed  are 
withdrawn.  Not  until  one  gets  back  his  bodily  reserve  is  he  able  to 
work  normally  and  effectively.  Increase  in  bodily  energy  comes  through 
health  and  not  through  the  use  of  stimulants. 

Summary.  —  The  body  requires  a  continuous  supply  of 
energy.  To  obtain  this  supply,  materials  possessing 
potential,  or  stored-up,  energy  are  introduced  into  it.  The 
free  oxygen  of  the  air  and  the  substances  known  as  foods, 
on  account  of  the  chemical  relations  which  they  sustain  to 
each  other,  contain  potential  energy  and  are  utilized  for 
supplying  the  body.  So  long  as  the  foods  are  not  oxi- 
dized, the  energy. remains  in  the  potential  form,  but  in 
the  process  of  oxidation  the  potential  energy  is  changed 
to  kinetic  energy  and  made  to  do  the  work  of  the  body. 

Exercises.  —  i.    In  what  different  ways  does  the  body  use  energy  ? 

2.    Show  that  a  stone  lying  against  the  earth  has  no  energy,  while 
the  same  stone  above  the  earth  has  energy. 


196  THE    VITAL   PROCESSES 

3.  How  does  potential  energy  differ  from  kinetic  energy  ? 

4.  What  kind  of  energy  is  possessed  by  a  bent  bow  ?     By  a  revolv- 
ing wheel?     By  a  coiled  spring  ?     By  the  wind  ?     By  gunpowder  ? 

5.  How  does  decomposing  water  with  electricity  store  energy  ? 

6.  Account  for  the  energy  possessed  by  the  oxygen  of  the  air  and 
food  substances. 

7.  Trace  the  energy  supply  of  the  body  back  to  the  sun. 

8.  Why  must  both  oxygen  and  food  be  introduced  into  the  body  in 
order  to  supply  it  with  energy  ? 

9.  How   may    overwork    and    overexercise   diminish   the   energy 
supply  of  the  body  ? 

10.    How  may  one  increase  the  amount  of  his  energy  ? 

PRACTICAL  WORK 

Suggested  Experiments.  —  i.  The  change  of  kinetic  into  potential 
energy  may  be  shown  by  stretching  a  piece  of  rubber,  by  lifting  a 
weight,  and  by  separating  the  armature  from  a  magnet. 

2.  The  change  of  potential  into  kinetic  energy  may  be  shown  by 
letting  weights  fall  to  the  ground,  by  releasing  the  end  of  a  piece  of 
stretched  rubber,  and  by  burning  substances. 

3.  The  change  of  one  form  of  kinetic  energy  to  another  may  be  il- 
lustrated by  rubbing  together  two  pieces  of  wood  until  they  are  heated, 
by  ringing  a  bell,  and  by  causing  motion  in  air  or  in  water  by  heating 
them.     If  suitable  apparatus  is  at  hand,  the  transformation  of  electrical 
energy  into  heat,  light,  sound,  and  mechanical  motion  can  easily  be 
shown. 

4.  A  weight  connected  by  a  cord  with  some  small  machine  and 
made  to  run  it,  will  help  the  pupil  to  grasp  the  general  principles  in  the 
storage  of  energy  through  gravity.     A  vessel  of  water  on  a  high  support 
from  which  the  water  is  siphoned  on  to  a  small  water  wheel  will  serve 
the  same  purpose. 

5.  The  storing  of  energy  by  chemical  means  may  be  illustrated  by 
decomposing  potassium  chlorate  with  heat  or  by  decomposing  water  by 
means  of  a  current  of  electricity. 

6.  Study  the  transfer  of  energy  from  the  body  to  surrounding  ob- 
jects, as  in  moving  substances  and  lifting  weights. 

Fill  a  half  gallon  jar  two  thirds  full  of  water  and  carefully  take  the 
temperature  with  a  chemical  thermometer.  Hold  the  hand  in  the  wat^r 
for  four  or  five  minutes  and  take  the  temperature  again.  Inference. 


CHAPTER   XIII 
GLANDS  AND  THE  WORK  OF  EXCRETION 

IN  our  study  so  far  we  have  been  concerned  mainly 
with  the  introduction  of  materials  into  the  body.  We  are 
now  to  consider  the  removal  of  materials  from  the  body. 
The  structures  most  directly  concerned  in  this  work  are 
known  as 

Glands. — As  generally  understood,  glands  are  organs 
that  prepare  special  liquids  in  the  body  and  pour  them  out 
upon  free  surfaces.  These  liquids,  known  as  secretions, 
are  used  for  protecting  exposed  parts,  lubricating  surfaces 
that  rub  against  each  other,  digesting  food,  and  for  other 
purposes.  They  differ  widely  in  properties  as  well  as  in 
function,  but  are  all  alike  in  being  composed  chiefly  of 
water.  The  water,  in  addition  to  being  necessary  to  the 
work  of  particular  fluids,  serves  in  all  cases  as  a  carrier  of 
solid  substances  which  are  dissolved  in  it. 

General  Structure  of  Glands.  —  While  the  various  glands 
differ  greatly  in  size,  form,  and  purpose,  they  present  strik- 
ing similarities  in  structure.  All  glands  contain  the  follow- 
ing parts : 

r.  Gland,  or  secreting,  cells.  These  are  specialized  cells 
for  the  work  of  secretion  and  are  the  active  agents  in 
the  work  of  the  gland.  They  are  usually  cubical  in  shape. 

2.  A  basement  membrane.     This  is  a  thin,  connective 
tissue  support  upon  which  the  secreting  cells  rest. 

3.  A  network  of  capillary  and  lymph  vessels.     These 

197 


I98  THE   VITAL   PROCESSES 

penetrate  the  tissues  immediately  beneath  the  secreting 
cells. 

4.  A  system  of  nerve  fibers  which  terminate  in  the  se- 
creting cells  and  in  the  walls  of  the  blood  vessels  passing 
to  the  glands. 

These  structures  —  secreting  cells,  basement  membrane, 
capillary  and  lymph  vessels,  and  nerve  fibers  —  form  the 
essential  parts  of  all  glands.  The  capillaries  and  the  lymph 
vessels  supply  the  secreting  cells  with  fluid,  and  the  nerves 
control  their  activities. 

Kinds  of  Glands.  —  Glands  differ  from  one  another  chiefly 
in  the  arrangement  of  their  essential  parts.1  The  most 
common  plan  is  that  of  arranging  the  parts  around  a  cen- 
tral cavity  formed  by  the  folding  or  pitting  of  an  exposed 
surface.  Many  such  glands  are  found  in  the  mucous 
membrane,  especially  that  lining  the  alimentary  canal,  and 
are  most  numerous  in  the  stomach,  where  they  supply 
the  gastric  juice.  If  these  glands  have  the  general  form 
of  tubes,  they  are  called  tubular  glands;  if  sac-like  in 
shape,  they  are  called  saccular  glands.  Both  the  tubular 
and  the  saccular  glands  may,  by  branching,  form  a  great 
number  of  similar  divisions  which  are  connected  with  one 
another,  and  which  communicate  by  a  common  opening 
with  the  place  where  the  secretion  is  used.  This  forms  a 
compound  gland  which,  depending  on  the  structure  of  the 
minute  parts,  may  be  either  a  compound  tubular  or  a  com- 
pound saccular  gland.  The  larger  of  the  compound  saccu- 
lar glands  are  also  called  racemose  glands,  on  account  of 
their  having  the  general  form  of  a  cluster,  or  raceme,  sim- 

1  The  simplest  arrangement  of  the  parts  of  a  gland  is  that  where  they  are  spread 
over  a  plain  surface.  This  arrangement  is  found  in  serous  membranes,  such  as 
the  pleura  and  peritoneum.  These  membranes,  however,  are  not  called  glands, 
but  secreting  surfaces. 


GLANDS   AND   THE   WORK   OF   EXCRETION 


199 


ilar  to  that  of  a  bunch  of  grapes.     The  general  structure 
of  the  different  kinds  of  glands  is  shown  in  Fig.  85. 


FIG.  85.  —  Diagram  illustrating  evolution  of  glands.  A.  Simple  secret- 
ing surface,  i.  Gland  cells.  2.  Basement  membrane.  3.  Blood  vessel. 
4.  Nerve.  B.  Simple  tubular  gland.  C.  Simple  saccular  gland.  D.  Com- 
pound tubular  gland.  E.  Compound  saccular  gland.  F.  A  compound  race- 
mose gland  with  duct  passing  to  a  free  surface.  G.  Relation  of  food  canal 
to  different  forms  of  glands.  The  serous  coat  has  a  secreting  surface. 

Nature  of  the  Secretory  Process.  —  At  one  time  the  gland 
was  regarded  merely  as  a  kind  of  filter  which  separated 
from  the  blood  the  ingredients  found  in  its  secretions. 
Recent  study,  however,  of  several  facts  relating  to  secre- 
tion has  led  to  important  modifications  of  this  view.  The 
secretions  of  many  glands  are  known  to  contain  substances 
that  are  not  found  in  the  blood,  or,  if  present,  are  there  in 
exceedingly  small  amounts.  Then  again  the  cells  of  cer- 
tain glands  have  been  found  to  undergo  marked  changes 
during  the  process  of  secretion.  If,  for  example,  the 


200 


THE   VITAL   PROCESSES 


cells  of  the  pancreas  be  examined  after  a  period  of  rest, 
they  are  found  to  contain  small  granular  bodies.  On 
the  other  hand,  if  they  are  examined  after  a  period  of 
activity,  the  granules  have  disappeared  and  the  cells  them- 
selves have  become  smaller  (Fig.  86).  The  granules  have 
no  doubt  been  used  up  in  forming  the  secretion.  These 


FIG.  86.  —  Secreting  cells  from  the  pancreas  (after  Langley).  A.  After 
a  period  of  rest.  B.  After  a  short  period  of  activity.  C.  After  a  period  of 
prolonged  activity.  In  A  and  B  the  nuclei  are  concealed  by  the  granules 
that  accumulate  during  the  resting  period. 

and  other  facts  have  led  to  the  conclusion  that  secretion  is, 
in  part,  the  separation  of  materials  without  change  from 
the  blood,  and,  in  part,  a  process  by  which  special  sub- 
stances are  prepared  and  added  to  the  secretion.  Accord- 
ing to  this  view  the  gland  plays  the  double  role  of  a.  filtering 
apparatus  and  of  a  manufacturing  organ. 

Kinds  of  Secretion.  —  In  a  general  way  all  the  liquids  pro- 
duced by  glands  may  be  considered  as  belonging  to  one  or 
the  other  of  two  classes,  known  as  the  useful  and  the  use- 
less secretions.  To  the  first  class  belong  all  the  secretions 
that  serve  some  purpose  in  the  body,  while  the  second 
includes  all  those  liquids  that  are  separated  as  waste  from 
the  blood.  The  first  are  usually  called  true  secretions,  or 
secretions  proper,  while  the  second  are  called  excretions. 
The  most  important  glands  producing  liquids  of  the  first 
class  are  those  of  digestion  (Chapter  X). 


GLANDS  AND  THE  WORK  OF  EXCRETION    2OI 

Excretory  Work  of  Glands.  — The  process  of  removing 
wastes  from  the  body  is  called  excretion.  While  in  theory 
excretion  may  be  regarded  as  a  distinct  physiological  act, 
it  is,  in  fact,  leaving  out  the  work  of  the  lungs,  but  a  phase 
of  the  work  of  glands.  From  the  cells  where  they  are 
formed,  the  waste  materials  pass  into  the  lymph  and  from 
the  lymph  they  find  their  way  into  the  blood.  They  are 
removed  from  the  blood  by  glands  and  then  passed  to  the 
exterior  of  the  body. 

The  Necessity  for  Excretion  is  found  in  the  results  at- 
tending oxidation  and  other  chemical  changes  at  the  cells 
(page  107).  Through  these  changes  large  quantities  of 
materials  are  produced  that  can  no  longer  take  any  part 
in  the  vital  processes.  They  correspond  to  the  ashes  and 
gases  of  ordinary  combustion  and  form  wastes  that  must 
be  removed.  The  most  important  of  these  substances, 
as  already  noted  (page  1 10),  are  carbon  dioxide,  water,  and 
urea.1  A  number  of  mineral  salts  are  also  to  be  included 
with  the  waste  materials.  Some  of  these  are  formed  in 
the  body,  while  others,  like  common  salt,  enter  as  a  part 
of  the  food.  They  are  solids,  but,  like  the  urea,  leave  the 
body  dissolved  in  water. 

Waste  products,  if  left  in  the  body,  interfere  with  its 
work  (some  of  them  being  poisons),  and  if  allowed  to  accu- 
mulate, cause  death.  Their  removal,  therefore,  is  as  im- 
portant as  the  introduction  of  food  and  oxygen  into  the 
body.  The  most  important  of  the  excretory  glands  are 

The  Kidneys.  — 'The  kidneys  are  two  bean-shaped  glands, 
situated  in  the  back  and  upper  portion  of  the  abdominal 

1  In  the  oxidations  that  occur  in  the  body  it  is  not  supposed  that  the  nutrients 
are  immediately  converted  to  carbon  dioxide,  water,  and  urea.  On  the  other  hand, 
it  is  held  that  their  reduction  takes  place  gradually,  as  the  reduction  of  sugar  by 
fermentation,  and  that  the  wastes  leaving  the  body  are  but  the  "  end  products  "  and 
show  only  the  final  results. 


2O2 


THE   VITAL   PROCESSES 


cavity,  one  on  each  side  of  the  spinal  column.  They 
weigh  from  four  to  six  ounces  each,  and  lie  between  the 

abdominal  wall  and  the  peri- 
toneum. Two  large  arteries  from 
the  aorta,  called  the  renal  arteries, 
supply  them  with  blood,  and  they 
are  connected  with  the  inferior 
vena  cava  by  the  renal  veins. 
They  remove  from  the  blood  an 
exceedingly  complex  liquid,  called 
the  urine,  the  principal  constituents 
of  which  are  water,  salts  of  dif- 
ferent kinds,  coloring  matter,  and 
urea.  The  kidneys  pass  their 
secretion  by  two  slender  tubes,  the 
ureters,  to  a  reservoir  called  the 
bladder  (Fig.  87). 

Structure    of    the    Kidneys.  — 
FIG.  87.  —  Relations  of  the   Each  kidney  is  a  compound  tubu- 
kidneys.      (Back  view.)       i.    kr     land  and  ig  composed   chiefly 
The   kidneys.     2.  Ureters.     3.       .    .  .     J 

Bladder.     4.  Aorta.    5.   In-  of  the  parts  concerned  in  secretion. 

The  ureter  serves  as  a  duct  for 
removing  the  secretion,  while  the 
blood  supplies  the  materials  from 

which  the  secretion  is  formed.  On  making  a  longitudinal 
section  of  the  kidney,  the  upper  end  of  the  ureter  is 
found  to  expand  into  a  basin-like  enlargement  which  is 
embedded  in  the  concave  side  of  the  kidney.  The  cavity 
within  this  enlargement  is  called  the  pelvis  of  the  kidney, 
and  into  it  project  a  number  of  cone-shaped  elevations 
from  the  kidney  substance,  called  the  pyramids  (Fig.  88). 

From  the  summits  of  the  pyramids  extend  great  num- 
bers of  very  small  tubes  which,  by  branching,  penetrate  to 


ferior  vena  cava.     6.  Renal 
arteries.    7.  Renal  veins. 


GLANDS  AND  THE  WORK  OF  EXCRETION    203 


all  parts  of  the  kidneys.  These  are  the  uriniferotts  tubules, 
and  they  have  their  beginnings  at  the  outer  margin  of  the 
kidney  in  many  small,  rounded  bodies  called  the  Malpighian 
capsules  (A,  Fig.  88).  Each  capsule  incloses  a  cluster  of 
looped  capillaries  and  connects  with  a  single  tubule  (Fig. 
89).  From  the  capsule  the  tubule  extends  toward  the  con- 


FIG.  88.  —  Sectional  view  of 
kidney,  i.  Outer  portion  or  cortex. 
2.  Medullary  portion.  3.  Pyramids. 
4.  Pelvis.  5.  Ureter.  A,  Small  sec- 
tion enlarged  to  show  the  tubules  and 
their  connection  with  the  capsules. 


FIG.  89.  —  Malpighian  cap- 
sule highly  magnified  (Landois). 
a.  Small  artery  entering  capsule 
and  forming  cluster  of  capillaries 
within.  e.  Small  vein  leaving 
capsule  and  branching  into  c,  a 
second  set  of  capillaries,  h.  Be- 
ginning of  uriniferous  tubule. 


cave  side  of  the  kidney  and,  after  uniting  with  similar 
tubules  from  other  parts,  finally  terminates  at  the  pyramid. 
Between  its  origin  and  termination,  however,  are  several 
convolutions  and  one  or  more  loops  or  turns.  After  pass- 
ing a  distance  many  times  greater  than  from  the  surface 
to  the  center  of  the  kidney,  the  tubule  empties  its  contents 
into  the  expanded  portion  of  the  ureter. 


2O4 


THE   VITAL   PROCESSES 


The  uriniferous  tubules  are  lined  with  secreting  cells. 
These  differ  greatly  at  different  places,  but  they  all  rest 

upon  a  basement  membrane  and 
are  well  supplied  with  capillaries. 
These  cells  provide  one  means 
of  separating  wastes  from  the 
blood  (Fig.  90). 

Blood  Supply  to  the  Kidneys. 
—  The  method  by  which  the 
kidneys  do  their  work  is  sug- 
gested by  the  way  in  which  the 
blood  circulates  through  them. 
The  renal  artery  entering  each 
kidney  divides  into  four  branches 
and  these  send  smaller  divisions 
to  all  parts  of  the  kidney.  At 
the  outer  margin  of  the  kidney, 
called  the  cortex,  the  blood  is 

passed  through  two  sets  of  cap- 
FIG.  90—  Diagram  illustrat-    illarigSm       The    first    forms    the 
mg  renal  circulation,    i.  Branch 

from  renal  artery.  2.  Branch  clusters  in  the  Malpighian  Cap- 
from  renal  vein.  3.  Small  artery  Sules  and  receives  the  blood 

branches,  one  of  which  enters  a  directly   from    the   smallest   ar- 

Malpighian  capsule  (O-    6.  Small    ,  r~,  j      r 

.  tenes.      The    second    forms    a 

vein    leaving    the    capsule    and 

branching  into  the  capillaries  (7)   network  around  the  uriniferous 

which  surround  the  uriniferous  tubules  and  receives  the  blood 
tubules.  4.  Small  veins  which  which  hag  passed  from  the  Cap- 
receive  blood  from  the  second  set  .„  .  ,  , 

(       -n    •       c  T  u  i     u        illary  clusters  into  a  system  ot 

of   capillaries.     8.  Tubule   show- 
ing lining  of  secreting  cells.  small  veins  (Fig.  90).     From  the 

last  set  of  capillaries  the  blood 

is  passed  into  veins  which  leave  the  kidneys  where  the 
artery  branches  enter,  uniting  there  to  form  the  main  renal 
veins. 


GLANDS  AND  THE  WORK  OF  EXCRETION    205 

Work  of  the  Kidneys.  —  Why  should  the  blood  pass 
through  two  systems  of  capillaries  in  the  kidneys?  This 
is  because  the  separation  of  waste  is  done  in  part  by  the 
Malpighian  capsules  and  in  part  by  the  uriniferous  tubules. 
Water  and  salts  are  removed  chiefly  at  the  capsules,  while 
the  remaining  solid  constituents  of  the  urine  pass  through 
the  secreting  cells  that  line  the  tubules.  It  was  formerly 
believed  that  the  kidneys  obtained  their  secretion  by  a 
process  of  filtration  from  the  blood,  but  this  belief  has 
been  gradually  modified.  The  prevailing  view  now  is  that 
the  processes  of  .filtration  and  secretion  are  both  carried  on 
by  the  kidneys,  —  that  the  capillary  clusters  in  the  Mal- 
pighian bodies  serve  as  delicate  filters  for  the  separation  of 
water  and  salts,  while  the  secreting  cells  of  the  tubules 
separate  substances  by  the  process  of  secretion. 

On  account  of  the  large  volume  of  blood  passing  through  the  kidneys 
this  liquid  is  still  a  bright  red  color  as  it  flows  into  the  renal  veins  (Fig. 
90).  The  kidney  cells  require  oxygen,  but  the  amount  which  they 
remove  from  the  blood  is  not  sufficient  to  affect  its  color  noticeably. 
The  blood  in  the  renal  veins,  having  given  up  most  of  its  impurities 
and  still  retaining  its  oxygen,  is  considered  the  purest  blood  in  the  body. 

Urea  is  the  most  abundant  solid  constituent  of  the  urine 
and  is  the  chief  waste  product  arising  from  the  oxidation 
of  nitrogenous  substances  in  the  body.  Although  secreted 
by  the  cells  lining  the  uriniferous  tubules,  it  is  not  formed 
in  the  kidneys.  The  secreting  cells  simply  separate  it  from 
the  blood  where  it  already  exists.  The  muscles  also  have 
been  suggested  as  a  likely  source  of  urea,  for  here  the  pro- 
teids  are  broken  down  in  largest  quantities  ;  but  the  muscles 
produce  little  if  any  urea.  Its  production  has  been  found 
to  be  the  work  of  tJie  liver.  In  the  muscular  tissue,  and 
in  the  other  tissues  as  well,  the  proteids  are  reduced  to  a 
lower  order  of  compounds,  such  as  the  compounds  of 


206  THE   VITAL   PROCESSES 

ammonia,  which  pass  into  the  blood  and  are  then  taken  up 
by  the  liver.  By  the  action  of  the  liver  cells  these  are 
converted  into  urea  and  this  is  turned  back  into  the  blood. 
From  the  blood  the  urea  is  separated  by  the  secreting  cells 
of  the  kidneys. 

Work  of  the  Liver.  —  The  liver,  already  described  as  an 
organ  of  digestion  (page  152),  assists  in  the  work  of  excretion 
both1  by  changing  waste  nitrogenous  compounds  into  urea 
and  by  removing  from  the  blood  the  wastes  found  in  the 
bile.  While  the  chief  work  of  the  liver  is  perhaps  not 
that  of  excretion,  its  functions  may  here,  be  summarized. 
The  liver  is,  first  of  all,  a  manufacturing  organ,  producing, 
as  we  have  seen,  three  distinct  products  —  bile,  glycogen, 
and  urea.  On  account  of  the  nature  of  the  urea  and  the 
bile,  the  liver  is  properly  classed  as  an  excretory  organ; 
but  in  the  formation  of  the  glycogen  it  plays  the  part  of 
a  storage  organ.  Then,  on  account  of  the  use  made  of  the 
bile  after  it  is  passed  into  the  food  canal,  the  liver  is  also 
classed  as  a  digestive  organ.  These  different  functions 
make  of  the  liver  an  organ  of  the  first  importance. 

Excretory  Work  of  the  Food  Canal.  —  The  glands  con- 
nected with  the  food  canal,  other  .than  the  liver,  while 
secreting  liquids  that  aid  in  digestion,  also  separate  waste 
materials  from  the  blood.  These  are  passed  into  the  canal, 
whence  they  leave  "the  body  with  the  undigested  portions 
of  the  food  and  the  waste  from  the  liver.  Though  the 
nature  and  quantity  of  the  materials  removed  by  these 
glands  have  not  been  fully  determined,  recent  investiga- 
tions have  tended  to  enhance  the  importance  attached  to 
this  mode  of  excretion. 

The  Perspiratory  Glands. — The  perspiratory,  or  sweat, 
glands  are  located  in  the  skin.  They  belong  to  the  type 
of  simple  tubular  glands  and  are  very  numerous  over  the 


GLANDS   AND   THE  WORK   OF   EXCRETION        2O7 


entire  surface  of  the  body.     A  typical  sweat  gland  consists 
of   a  tube  which,  starting  at   the  surface  of   the  cuticle, 
penetrates  to  the  under  portion  of  the  true  skin  and  there 
forms  a  ball-shaped  coil.     The  coiled 
extremity,  which  forms  the  secreting 
portion,  is  lined  with  secreting  cells 
and  surrounded  by  a  network  of  capil- 
laries.    The  portion  of  the  tube  pass- 
ing from  the  coil  to  the  surface  serves 
as  a  duct  (Figs.  91  and  121). 

The  sweat  glands  secrete  a  thin, 
colorless  fluid,  called  perspiration,  or 
sweat.  This  consists  chiefly  of  water, 
but  contains  a  small  per  cent  of  salts 
and  of  urea.  The  excretory  work  of 
these  glands  seems  not  to  be  so  great 
as  was  formerly  supposed,  but  they 
supplement  in  a  practical  way  the 
work  of  the  kidneys  and,  during 
diseases  of  these  organs,  show  an  in- 
crease in  excretory  function  to  a 
marked  degree.  The 


b  \ 


FIG.    91.  —  Diagram 
of    section   through    a 
a.  Outer 


forming  the  coiled  portion 
of  the   gland.      c.  Duct 


perspiration    sweat  2land- 

also     aids     in     the     regulation     of     the     'ayer  of  skin  or  cuticle. 
0  b.  Dermis   or   true   skin. 

temperature    of    the    body   (Chapter   dj ,  sections  of  the  tube 
XVI). 

Excretory   Work   of    the    Lungs. 

IT 71  -i      ,i        -i  ,    i  ij     passing    to    the    surface. 

While  the  lungs  cannot  be  regarded    -T 

The  other  structures   of 

as  glands,  they  do  a  work  in  the  re-    the  skin  not  shown. 
moval  of  waste  from  the  body  which 
must  be  considered  in  the  general  process  of  excretion. 
They  are  especially  adapted  to  the  removal  of  gaseous 
substances  from  the  blood,  and  it  is  through  them  that 
most  of  the  carbon  dioxide  leaves  the  body.     The  lungs 


208  THE   VITAL   PROCESSES 

remove  also  a  considerable  quantity  of  water.     This  is  of 
course  in  the  gaseous  form,  being  known  as  water  vapor. 

Ductless  Glands  and  Internal  Secretion.  —  Midway  in  function  be- 
tween the  glands  that  secrete  useful  liquids  and  those  that  remove 
waste  materials  from  the  blood  is  a  class  of  bodies,  found  at  various 
places,  known  as  the  ductless  glands.  They  are  so  .named  from  their 
having  the  general  form  of  glands  and  from  the  fact  that  they  have 
no  external  openings  or  ducts.  They  prepare  special  materials  which 
are  passed  into  the  blood  and  which  are  supposed  to  exert  some  bene- 
ficial effect  either  upon  the  blood  or  upon  the  tissues  through  which 
the  blood  circulates.  The  most  important  of 'the  ductless  glands  are 
the  thyroid  gland,  located  in  the  neck ;  the  suprarenal  bodies,  situated 
one  just  over  each  kidney ;  and  the  thymus  gland,  a  temporary  gland 
in  the  upper  part  of  the  chest.  The  spleen  and  the  lymphatic  glands 
(page  68)  are  also  classed  with  the  ductless  glands.  The  liver,  the 
pancreas,  and  (according  to  some  authorities)  the  kidneys,  in  addition 
to  their  external  secretions,  produce  materials  that  pass  into  the  blood. 
They  perform  in  this  way  a  function  like  that  of  the  ductless  glands. 
The  work  of  glands  in  preparing  substances  that  enter  the  blood  is 
known  as  internal  secretion. 

Quantity  of  Excretory  Products.  —  If  the  weight  of  the 
normal  body  be  taken  at  intervals,  after  growth  has  been 
attained,  there  will  be  found  to  be  practically  no  gain  or 
loss  from  time  to  time.  This  shows  that  materials  are 
leaving  the  body  as  fast  as  they  enter  and  that  the  tissues 
are  being  torn  down  as  fast  as  they  are  built  up.  It  also 
shows  that  substances  do  not  remain  in  the  body  perma- 
nently, but  only  so  long  perhaps  as  is  necessary  for  them 
to  give  up  their  energy,  or  serve  some  additional  purpose 
in  the  ever  changing  protoplasm.  The  excretory  organs 
then  remove  from  the  body  a  quantity  of  material  that  is 
equal  in  weight  to  the  materials  absorbed  by  the  organs  of 
digestion  and  respiration.  This  is  estimated  for  the  aver- 
age individual  to  be  about  five  pounds  daily.  The  passage 
of  waste  from  the  body  is  summarized  in  Table  III. 


GLANDS    AND    THE    WORK    OF    EXCRETION 


209 


'     73      4) 

rt     4>     *~! 

o5  x 

x   c   a 

CJ     -t-1 

•s    <u 

'/! 

Q 
O 
O 

j=    o    o 

«   c  -2 

^2    "    73 
S     S     C 

C     rt 

"°  ^  ? 

.2* 

iJ 

m 

W 

X 
H 

rt     <U 

73  •£  £ 

0  -«    ^ 

§    M    bC 
0     rt     ^ 

^  2  o 

G      (LJ     "*"* 

rt     b/o  73 
bjQ   i-     O 

S^3   rt 

c 
rt 

S 

3    rt     J2 

'S    73      C 

4)      *>      >, 

,^ 

O 

-     C    *^ 

u 

• 

r^       hfl     ^^ 

3     rt     ^ 

•*-•     4~>     G 

h 

•*-•    c  .3 

"     t« 

—  '     G   S 

9 

Q 
> 

S  —    rt 

73     a?   CX 

'g.  —  3 

«T 

O 

o    <u    v    <u 

£J 

K           4-*         4} 

^> 

s 

H 

•*5  -5  •£    «j 

^.••B   ^ 

(•^      ^      <"•; 

G 

K 

73      lj_,        r-      J^ 

73  ^    *^ 

73        ^    >"> 

r2 

6 

K 

rt  '•§  2  1 

d.    1>     <-    ^H 

llf 

S  ^    S3 
~  ^g    <u 

4)      C    -Q 
>    .2      CO 

^,  2  :l 

4) 

a;    >   73     rt 

c/5 

M 

» 

PQ 

Q 

<u    D  jr 

O 

o 

f-i         C/^        -4—  •            . 

3 

^_.         S^         ^         ^ 

4) 

4) 

pa 

—  '             o 

-5 

^ 

Id 

.S  .2  fl  3 

h 

"O     o     W 

.2 

.2 

£5 

73     P    **~;    ^^ 

CONDITION  i 

m    rt    ^    *-• 
>     rt  .2     fl 

tn   —     o  13 

g-3,8  g 

j>   g 

O     in 

|t 

u 

1 

M 

Dissolved 
plasma. 

*°  S  j§ 

C      ' 

O     O     >>    M   .2 

Id 

o    </5 

X 

z 

o  > 

S       OH    "rt 

"rt          J3* 

e  £  -a 
o  .«    a 

•J     G      D 
rt  t..     O 

12   o   ^ 

rt     W)  rt   73     £     <« 

•9  2        9  t2  S3 

s  o 

KS 

o 

'3    O  ^ 
o  -£    |5    «; 

s  s  "-^ 

ofeo 

4)     "3       «5 

J3             3 

•^73   ^  rt      r 
,S     'S  J  S  i" 

o 
K 

"*^     ID   T3   73 
^.C    'S     S5 

•»    (i    Q 

K      -C      S3 

-*-1     4)    O    rt     g     «j 

>~>  TJ       &,  73     *^     " 

PQ  T  " 

Pq"  *" 

P3 

U 

T3 

73 

*s 

73 

1 

in 

rt 

O 

3 
w 

cr 

3 

3 
w 

73 

J 

"fij 

2 

O 

E 

Id 

73 

R 

C 
O 

L 

w 

rt 

-2d 

C/3 

u 

rt 

rt 

i_ 

rt 

U 

D 

* 

CO 

2io  THE   VITAL  PROCESSES 

HYGIENE 

The  separation  of  wastes  from  the  body  has  such  a  close 
relation  to  the  health  that  all  conditions  affecting  it  should 
receive  the  most  careful  attention.  Their  retention  beyond 
the  time  when  they  should  be  discharged  undoubtedly  does 
harm  and  is  the  cause  of  many  bodily  disorders. 

Value  of  Water.  —  As  a  rule  the  work  of  excretion  is 
aided  by  drinking  freely  of  pure  water.  As  water  is  the 
natural  dissolver  and  transporter  of  materials  in  the  body, 
it  is  generally  conceded  by  hygienists  and  physicians  that 
the  taking  of  plenty  of  water  is  a  healthful  practice.  Peo- 
ple do  not  as  a  rule  drink  a  sufficient  amount  of  water,  about 
three  pints  per  day  being  required  by  the  average  adult, 
in  addition  to  that  contained  in  the  food.  Most  of  the 
water  should,  of  course,  be  taken  between  meals,  although 
the  sipping  of  a  small  amount  during  meals  does  not 
interfere  with  digestion.  As  stated  elsewhere,  the  taking 
of  a  cup  of  water  on  retiring  at  night  and  again  on  rising 
in  the  morning  is  very  generally  recommended. 

Protection  of  Kidneys  and  Liver.  —  The  kidneys  and  liver 
are  closely  related  in  their  work  and  in  many  instances 
are  injured  or  benefited  by  the  same  causes.  Both, 
as  already  stated  (page  124),  are  liable  to  injury  from 
an  excess  of  proteid  food,  especially  meats,  and  also  by  a 
condition  of  inactivity  of  the  bowels  (page  166).  The 
free  use  of  alcohol  also  has  an  injurious  effect  on  both  of 
these  organs.1  On  the  other  hand,  increasing  the  activity 
of  the  skin  has  a  beneficial  effect  upon  them,  especially 

1  Alcohol,  if  used  in  considerable  quantity,  leads  to  cirrhosis  of  the  liver  and 
Bright's  disease  of  the  kidneys,  both  very  dangerous  diseases.  Dr.  William  Osier 
in  his  treatise,  The  Practice  of  Medicine,  states  that  alcohol  is  the  chief  cause  of 
cirrhosis  of  the  liver.  Dr.  T.  N.  Bogart,  specialist  in  kidney  diseases,  asserts  that 
one  third  of  all  the  cases  of  Bright's  disease  coming  under  his  observation  are 
caused  by  alcohol. 


GLANDS   AND   THE   WORK   OF   EXCRETION        211 

the  kidneys.  Exercise  and  bathing,  which  tend  to  make 
the  skin  more  active,  are  valuable  aids  both  in  ridding  the 
body  of  impurities  and  in  lessening  the  work  of  the  other 
excretory  organs.  One  having  a  disease  of  the  kidneys, 
however,  needs  to  exercise  great  care  in  bathing  on  account 
of  the  bad  results  which  follow  getting  chilled. 

Special  Care  after  Certain  Diseases.  —  Certain  diseases, 
as  measles,  diphtheria,  scarlet  fever,  and  typhoid  fever, 
sometimes  have  the  effect  of  weakening  the  kidneys  (and 
other  vital  organs)  and  of  starting  disease  in  them.  When 
this  occurs  it  is  usually  the  result  of  exposure  or  of  over- 
exertion  while  the  body  is  in  a  weakened  condition. 
Severe  chilling  at  such  a  time,  by  driving  blood  from  the 
surface  to  the  parts  within,  often  causes  inflammation  of 
the  kidneys.  On  recovering  from  any  wasting  disease  one 
should  exercise  great  caution  both  in  resuming  his  regular 
work  and  in  exposing  his  body  to  wet  or  cold. 

Misunderstood  Symptoms.  —  Pains  in  the  small  of  the 
back,  an  increase  in  the  secretions  of  the  kidneys,  and  a 
sediment  in  the  urine  very  naturally  suggest  some  disorder 
of  the  kidneys.  It  is  a  fact,  however,  that  these  symptoms 
have  little  or  no  relation  to  the  state  of  the  kidneys  and 
may  occur  when  the  kidneys  are  in  a  perfectly  healthy 
condition.  The  kidneys  are  not  located  in  the  small  of 
the  back,  but  above  this  place,  so  that  pains  in  this  region 
are  evidently  not  from  the  kidneys,  while  the  increase  in 
the  flow  of  the  urine  may  arise  from  a  number  of  causes, 
one  of  which  is  an  increase  of  certain  waste  products 
passed  into  the  blood.  The  symptoms  referred  to  are 
frequently  the  results  of  nervous  exhaustion,  resulting 
from  overstudy,  worry,  eye  strain,  or  some  other  condition 
that  overtaxes  the  nervous  system.  When  this  is  the  case, 
relief  is  obtained  through  resting  the  nerves.  Actual 


212  THE   VITAL    PROCESSES 

disease  of  the  kidneys  can  only  be  determined  through  a 
chemical  and  microscopic  examination  of  the  urine.  To 
resort  to  some  patent  medicine  for  kidney  trouble  without 
knowing  that  such  trouble  exists,  as  is  sometimes  done,  is 
both  foolish  and  unhygienic. 

Alcoholic  Beverages  and  the  Elimination  of  Waste. — Causing  as  it 
does  such  serious  diseases  as  cirrhosis  of  the  liver  and  Bright's  disease 
of  the  kidneys  (footnote,  page  210),  alcohol  will  greatly  interfere  in  this 
way  with  the  elimination  of  waste.  There  is  also  evidence  to  the  effect 
that  it  interferes  with  waste  elimination  before  the  stage  is  reached  of 
causing  disease  of  these  organs.  Researches  have  shown  that  alcohol 
increases  the  amount  of  uric  acid  in  the  body  and  decreases  the  amount 
of  urea  found  in  the  urine.  The  conclusion  to  be  drawn  is  that  alcohol 
interferes  in  some  way  with  the  change  of  the  harmful  uric  acid  into  the 
comparatively  harmless  urea  —  an  interference  which  in  some  instances 
results  in  great  harm.  It  has  also  been  shown  that  malted  liquors,  such 
as  beer  and  ale,  contain  substances  which,  like  the  caffein  of  tea  and 
coffee  (page  167),  are  readily  converted  into  uric  acid.1  Wines  contain 
acids  which  may  also  act  injuriously.  The  harm  which  such  substances 
do  is,  of  course,  additional  to  that  caused  by  the  alcohol. 

Summary.  —  As  a  result  of  the  oxidations  and  other 
changes  at  the  cells,  substances  are  produced  that  can  no 
longer  serve  a  purpose  in  the  body.  They  are  of  the 
nature  of  waste,  and  their  continuous  removal  from  the 
body  is  as  necessary  to  the  maintenance  of  life  as  the  in- 
troduction of  food  and  oxygen.  The  organs  whose  work  it 
is  to  remove  the  waste,  excepting  the  lungs,  are  glands  ;  and 
the  material  which  they  remove  are  of  the  nature  of  secre- 
tions. From  the  cells,  the  waste  passes  through  the  lymph 
in  the  blood.  From  the  blood  it  is  separated  by  the  excre- 
tory organs  and  passed  to  the  exterior  of  the  body. 

Exercises.  —  i.  What  general  purposes  are  served  by  the  glands  in 
the  body  ? 

*  1  Hall,  The  Purin  Bodies. 


GLANDS   AND   THE  WORK    OF    EXCRETION        213 

2.  What  are  the  parts  common  to  all  glands  ?     What  purpose  is 
served  by  each  of  these  parts  ? 

3.  How  do  tubular  glands  differ  in  structure  from  saccular  glands  ? 
What  is  a  racemose  gland  ?     Why  so  called  ? 

4.  Describe  the  nature  of  the  secretory  process. 

5.  What  conditions  render  necessary  the  formation  of  waste  mate- 
rials in  the  body  ?     Why  must  these  be  removed  ? 

6.  How  do  the  waste  materials  get  from  the  cells  to  the  organs  of 
excretion  ? 

7.  Show  by  a  drawing  the  connections  of  the  kidneys  with  the 
large  blood  vessels  and  the  bladder.     Name  parts  of  drawing. 

8.  In   what  do  the  uriniferous  tubes  have  their  beginning  ?     In 
what  do  they  terminate  ?     With  what  are  they  lined  ? 

9.  Why  should  the  blood  pass  through  two  sets  of  capillaries  in 
the  kidneys  ? 

10.  Bright's  disease  of  the  kidneys  affects  the  uriniferous  tubes  and 
interferes  with  their  work.     What  impurity  is  then  left  in  the  blood  ? 

11.  Trace  water  and    salts    from  the    Malpighian    capsules   to  the 
bladder,  naming  parts  through  which  they  pass. 

12.  Trace  carbon  dioxide  from  the  cells  to  the  outside  atmosphere. 

13.  How  does  the  quantity  of  material  introduced  into  the  body 
compare  with  that  which  is  removed  by  the  organs  of  excretion? 

14.  Name  two  ways  of  lessening  the  work  of  the  kidneys. 

15.  Why  is  the  drinking  of  plenty  of  pure  water  a  healthful  prac- 
tice? 

PRACTICAL  WORK 

To  suggest  the  Double  Work  of  Glands.  —  Prepare  a  simple  filter  by 
fitting  a  piece  of  porous  paper  into  a  glass  funnel.  Through  this  pass 
pure  water  and  also  water  having  salt  dissolved  in  it  and  containing 
some  sediment,  as  sand.  The  water  and  the  dissolved  salt  pass  through, 
while  the  sediment  remains  on  the  filter.  Now  substitute  a  fresh  piece 
of  paper  in  the  funnel  and  drop  on  its  surface  a  little  solid  coloring 
matter,  such  as  cochineal.  Again  pass  the  liquid  through  the  funnel. 
This  time  it  comes  through  colored,  the  color  being  added  by  the 
filter.  Compare  the  filter  and  materials  filtered  to  the  gland  and  the 
materials  concerned  in  secretion  (blood,  the  liquid  secreted,  substances 
added  by  the  gland,  etc.). 


214 


THE   VITAL  PROCESSES 


FIG.  92. —  The  physiological  scheme.  Diagram  suggesting  the  essential 
relation  of  the  bodily  activities.  See  Summary  of  Part  I,  page  215,  and 
Summary  of  Part  II,  page  413. 


SUMMARY   OF  PART  I  215 

SUMMARY   OF   PART   I 

The  body  is  an  organization  of  different  kinds  of  cells ; 
it  grows  through  the  growth  and  reproduction  of  these 
cells ;  and  its  life  as  a  whole  is  maintained  by  providing 
such  conditions  as  will  enable  the  cells  to  keep  alive.  Of 
chief  importance  in  the  work  of  the  body  is  a  nutrient  fluid 
which  supplies  the  cells  with  food  and  oxygen  and  relieves 
them  of  waste.  A  moving  portion  of  this  fluid,  called 
the  blood,  serves  as  a  transporting  agent,  while  another 
portion,  called  the  lymph,  passes  the  materials  between 
the  blood  and  the  cells.  Through  their  effects  upon  the 
blood  and  the  lymph,  the  organs  of  circulation,  respiration, 
digestion,  and  excretion  minister  in  different  ways  to  the 
cells,  and  aid  in  the  maintenance  of  life.  By  their  com- 
bined action  two  distinct  movements  are  kept  up  in  the 
body,  as  follows : 

1.  An  inward  movement  which  carries  materials  from 
the  outside  of  the  body  toward  the  cells. 

2.  An  outward  movement  which  carries  materials  from 
the  cells  to  the  outside  of  the  body. 

Passing  inward  are  the  oxygen  and  food  materials  in  a 
condition  to  unite  with  each  other  and  thereby  change  their 
potential  into  kinetic  energy.  Passing  outward  are  the 
oxygen  and  the  elements  that  formed  the  food  materials 
after  having  united  at  the  cells  and  liberated  their  energy. 

As  a  final  and  all-important  result,  there  is  kept  up  a 
continuous  series  of  chemical  changes  in  the  cells.  These 
liberate  the  energy,  provide  special  substances  needed  by 
the  cells,  and  preserve  the  life  of  the  body  (Fig.  92). 

In  the  chapters  which  follow,  we  are  to  consider  the 
problem  of  adjusting  the  body  to  and  of  bringing  it  into 
proper  relations  with  its  surroundings. 


PART    II:     MOTION,    COORDINATION, 
AND   SENSATION 

CHAPTER  XIV 
THE  SKELETON 

ONE  necessary  means  of  establishing  proper  relations 
between  the  body  and  its  surroundings  is  motion^  Not 
only  can  the  body  move  itself  from  place  to  place,  but  it 
is  able  to  move  surrounding  objects  as  well.  In  the  pro- 
duction of  motion  three  important  systems  are  employed 
— •  the  muscular  system,  the  nervous  system,  and  a  system 
of  mechanical  devices  which  are  found  mainly  in  the 
skeleton.  The  muscular  system  supplies  the  energy  for 
operating  the  mechanical  devices,  while  the  nervous  system 
controls  the  movements.2  Although  the  skeleton  serves 
other  purposes,  such  as  giving  shape  to  the  body  and  pro- 
tecting certain  organs,  its  main  use  is  that  of  an  aid  in  the 
production  of  motion. 

1  Review  "  Main  Physiological  Problems,"  page  21. 

2  In  the  production  of  motion  in  the  body,  as  well  as  in  the  production  of  any 
kind  of  purposeful  motion  outside  of  the  body,  three  conditions  must  be  fulfilled. 
There  is  required,  in  the  first  place,  a  mechanical  device  or  machine  which  is  so 
constructed  as  to  produce  a  certain  kind  of  motion.     In  the  second  place,  energy 
is  needed  to  operate  this  device.    And,  finally,  there  must  be  some  controlling 
force,  by  means  of  which  the  motion  is  made  to  accomplish  definite  results.    The 
driving  of  a  horse  hitched  to  a  wagon  will  illustrate  these  conditions.    The  wagon 
is  the  mechanical  device,  the  horse  furnishes  the  energy,  and  the  driver  supplies 
the  controlling  force.      In   this,  as  in  most  cases,  the  machinery,  the  source  of 
energy,  and  the  controlling  force  are  disconnected  except  when  at  work;  butin  the 
body  all  three  occur  together  in  the  same  structure. 

216 


THE    SKELKTON 

Skeleton  Tissues.  —  The  tissues  employed  in  the  con- 
struction of  the  skeleton  are  the  osseous,  the  cartilaginous, 
and  the  connective  tissues.  These  are  known  as  the  sup- 
porting tissues  of  the  body.  They  form  the  bones,  supply 
the  elastic  pads  at  the  ends  of  the  bones,  and  furnish 
strong  bands,  called  ligaments,  for  fastening  the  bones 
together.  The  skeleton  forms  about  16  per  cent  of  the 
weight  of  the  body.  Its  tissues,  being  of  a  more  durable 
nature  than  the  rest  of  the  body,  do  not  so  readily  decay. 
Especially  is  this  true  of  the  osseous  tissue,  which  may  be 
preserved  indefinitely,  after  removal  from  the  body,  by 
simply  keeping  it  dry. 

The  Bones.  —  The  separate  units,  or  parts,  of  which  the 
skeleton  is  constructed  are  called  bones.  They  are  the 
hard  structures  that  can  be  felt  in  all  parts  of  the  body, 
and  they  comprise  nearly  the  entire  amount  of  material 
found  in  the  prepared  skeleton.  As  usually  estimated, 
the  bones  are  208  in  number.  They  vary  greatly  in  size 
and  shape  in  different  parts  of  the  body. 

Composition  and  Properties  of  Bones.  —  The  most  notice- 
able and  important  properties  of  the  bones  are  those  of 
hardness,  stiffness,  and  toughness.  Upon  these  properties 
the  uses  of  the  bones  depend.  These  properties  may,  in 
turn,  be  shown  to  depend  upon  the  presence  in  osseous 
tissue  of  two  essentially  different  kinds  of  substance, 
known  as  the  animal  matter  and  the  mineral  matter.  If  a 
bone  is  soaked  in  an  acid,  the  mineral  matter  is  dissolved 
out,  and  as  a  result  it  loses  its  properties  of  hardness  and 
stiffness.  (See  Practical  Work.)  This  is  because  the  min- 
eral matter  supplies  these  properties,  being  composed  of 
substances  which  are  hard  and  closely  resemble  certain 
kinds  of  rock.  The  chief  materials  forming  the  mineral 
matter  are  calcium  phosphate  and  calcium  carbonate. 


MOTION   AND   COORDINATION 


On  the  other  hand,  burning  a  bone  destroys  the  animal 
matter.  When  this  is  done  the  bone  loses  its  toughness, 
and  becomes  quite  brittle.  The  prop- 
erty of  toughness  is,  therefore,  sup- 
plied by  the  animal  matter.  This 
consists  mainly  of  a  substance  called 
ossein,  which  may  be  dissolved  out  of 
the  bones  by  boiling  them.  Sepa- 
rated from  the  bones  it  is  known  as 
gelatine.  The  blood  vessels  and 
nerves  in  the  bones,  and  the  pro- 
toplasm of  the  bone  cells,  are  also 
counted  in  with  the  animal  matter. 

If  a  dry  bone  from  a  full-grown,  but 
not  old,  animal  be  weighed  before  and 
after  being  burned,  it  is  found  to  lose 
about  one  third  of  its  weight.  From 
this  we  may  conclude  that  about  one 
third  of  the  bone  by  weight  is  animal 
matter  and  two  thirds  is  mineral 
matter.  This  proportion,  however, 
varies  with  age,  the  mineral  matter 
increasing  with  advance  of  years. 

Gross  Structure  of  Bones.  —  The 
gross  structure  of  the  bones  is  best 
learned  by  studying  both  dry  and 
fresh  specimens.  (See  Practical 
Work.)  The  ends  of  the  bones  are 
capped  by  a  layer  of  smooth,  elastic 
cartilage,  while  all  the  remaining  sur- 

FIG.  93. -Section  of  faCG  ls  covered  bY  a  rather  dense 
a  long  bone  (tibia),  show-  sheath  of  connective  tissue,  called  the 
ing  the  gross  structure.  periosteum.  Usually  the  central  part 


THE   SKELETON 


219 


of  the  long  bones  is  hollow,  being  filled  with  a  fatty 
substance  known  as  the  yellow  marrow.  Around  the 
marrow  cavity  the  bone  is  very  dense  and  compact,  but 
most  of  the  material  forming  the  ends  is  porous  and 
spongy.  These  materials  are  usually  referred  to  as  the 
compact  substance  and  the  cancellous,  or  spongy,  substance  of 
the  bones  (Fig.  93). 

The  arrangement  of  the  compact  and  spongy  substance 
varies  with  the  different  bones.  In  the  short  bones  (wrist 
and  ankle  bones,  vertebras,  etc.) 
and  also  in  the  flat  bones  (skull 
bones,  ribs,  shoulder  blades,  etc.) 
there  is  no  cavity  for  the  yellow 
marrow,  all  of  the  interior  space 
being  filled  with  the  spongy  sub- 
stance. The,  red  marroiv,  rela- 
tions of  which  to  the  red  cor- 
puscles of  the  blood  have  already 
been  noted  (page  27),  occupies 
the  minute  spaces  in  the  spongy 
substance. 

Minute  Structure  of  Bone.  — 
A  microscopic  examination  of  a 
thin  slice  of  bone  taken  from  the 
compact  substance  shows  this  to 
be  porous  as  well  as  the  spongy 
substance.  Two  kinds  of  small 
channels  are  found  running 
through  it  in  different  directions, 
known  as  the  Haversian  canals 
and  the  canaliculi  (Fig.  94). 


FIG.  94.  —  Cross  section  of 
bone  showing  minute  structure. 
Magnified,  i.  Surface  layer  of 
bone.  2.  Deeper  portion.  3.  Ha- 
versian canals  from  which  pass 
the  canaliculi.  4.  A  lacuna.  Ob- 
serve arrangement  of  lacunae  at 
surface  and  in  deeper  portion. 


These  serve  the  general  purpose  of  distributing  nourish- 
ment through  the  bone.     The  Haversian  canals  are  larger 


22O 


MOTION    AND   COORDINATION 


than  the  canaliculi  and  contain  small  nerves  and  blood 
vessels,  chiefly  capillaries  (Fig.  95).  They  extend  length- 
wise through  the  bone.  The  canaliculi  are  channels  for 
conveying  lymph.  They  pass  out  from  the  Haversian 
canals  at  right  angles,  going  to  all  por- 
tions of  the  compact  substance  except  a 
thin  layer  at  the  surface.  In  the  surface 
layer  of  the  bone  the  canaliculi  are  in 
communication  with  the  periosteum. 
The  Bone  Cells.  —  Surrounding  the 

Haversian  canals  are  thin  layers  of  bone 
showing  Haversian 

canal  and  contents,  substance  called  the  lamina,  and  within 
highly  magnified  (af-  these  are  great  numbers  of  irregular 
terSchafer).  i.  Arterial  bodieS)  known  as  the  lacunce.  The  walls 

capillary!  ^NewT  of  the  lacunse  are  hard  and  dense,  but 
bers.  4.  Lymph  vessel,  within  each  is  an  open  space.  In  this 
lies  a  flattened  body,  having  a  nucleus, 
which  is  recognized  as  the  bone  cell,  or  the  bone  corpuscle 
(Fig.  96).  It  appears  to  be  the  work  of  the  bone  cells  to 
deposit  mineral  matter  in  the  walls 
surrounding  them  and  in  this  way  to 
supply  the  properties  of  hardness  and 
stiffness  to  the  bones.  The  canaliculi 
connect  with  the  lacunae  in  all  parts 

of  the  bone,  causing  them  to  appear 

FIG.  96.  —  Bone  cell 
under   the   microscope    like   so   many   removed  from  the  lacuna 

burs  fastened  together  by  their  pro-  and  very  highly  magni- 
jecting  spines  (Fig.  94).  fied-  (From  Quain's 

How  the  Bone  Cells  are  Nourished.  - 

The  bone  cells,  like  all  the  other  cells  of  the  body,  are 
nourished  by  the  lymph  that  escapes  from  the  blood. 
This  passes  through  the  canaliculi  to  the  cells  in  the  dif- 
ferent parts  of  the  bone,  as  follows : 


THE    SKELETON  221 

1.  The  cells  in  the  surface  layer  of  the  bone  receive 
lymph  from  the  capillaries  in  the  periosteum.1     It  gets  to 
them  through  the  short  canaliculi  that  run  out  to  the  surface. 

2.  The  cells  within  the  interior  of  the  bone  receive  their 
nourishment  from  the  small  blood  vessels  in  the  Haversian 
canals.     Lymph  from  these  vessels  is  conveyed  to  the  cells 
through  the  canaliculi  that  connect  with  the  Haversian 
canals. 

Plan  and  Purpose  of  the  Skeleton.  —  The  framework  of 
the  body  is  such  as  to  adapt  it  to  a  movable  structure. 
Obviously  the  different  parts  of  the  body  cannot  be  secured 
to  a  foundation,  as  are  those  of  a  stationary  building,  but 
must  be  arranged  after  a  plan  that  is  conducive  to  motion. 
A  moving  structure,  as  a  wagon  or  a  bicycle,  has  within  it 
some  strong  central  part  to  which  the  remainder  is  joined. 
The  same  is  true  of  the  skeleton.  That  part  to  which  the 
others  are  attached  is  a  long,  bony  axis,  known  as  the 
spinal  column.  Certain  parts,  as  the  ribs  and  the  skull,  are 
attached  directly  to  the  spinal  column,  while  others  are  at- 
tached indirectly  to  it.  The  arrangement  of  all  the  parts 
is  such  that  the  spinal  column  is  made  the  central,  cohering 
portion  of  the  skeleton  and  also  of  the  whole  body. 

Besides  the  general  arrangement  of  the  parts  of  the 
skeleton,  there  is  such  a  grouping  of  the  bones  in  each  of 
its  main  divisions  as  will  enable  them  to  serve  definite  pur- 
poses. In  most  places  they  form  mechanical  devices 
for  supplying  special  movements,  and  in  certain  places 
they  provide  for  the  support  or  protection  of  important 
organs.  In  most  cases  there  is  a  definite  combination  of 
different  bones,  forming  what  is  called  the  bone  group. 

l  The  dependence  of  the. outer  layers  of  hone  cells  upon  the  periosteum  for 
nourishment  causes  a  destruction  of  this  membrane  to  affect  seriously  the  bone 
beneath,  producing  in  many  instances  a  decay  of  the  bone  substance. 


222  MOTION    AND   COORDINATION 

Frontal.. .A 


•Superior     

MaxiJlary 

Scapula 


Hume 


Radius 


FIG.  97.  —  The  human  skeleton. 


THE    SKELETON 


223 


Bone  Groups.  —  On  account  of  the  close  relation  between 
the  bones  of  the  same  group,  they  cannot  profitably  be 
studied  as  individual  bones,  but  each 
must  be  considered  as  a  part  of  the 
group  to  which  it  belongs.      By  first 
making  out  the  relation  of  a  given  bone 
to  its  group,  its  value  to  the  whole  body 
can  be  determined.    The  most  important 
of  the  groups  of  bones  are  as  follows : 

i .  The  Spinal  Column.  — This  group 
consists  of  twenty-four  similarly  shaped 
bones,  placed  one  above  the  other, 
called  the  vertebra,  and  two  bones 
found  below  the  vertebrae,  known  as 
the  sacrum  and  the  coccyx  (Fig.  98). 
These  twenty-six  bones  supply  the 
central  axis  of  the  body,  support  the 
head  and  upper  extremities,  and  in- 
close and  protect  the  spinal  cord. 

The  upper  seven  vertebrae  form  the 
neck  and  are  called  the  cervical  ver- 
tebrae. They  are  smaller  and  have 
greater  freedom  of  motion  than  the 
others.  The  first  and  second  cervical 
vertebrae,  known  as  the  atlas  and  the 
axis,  are  specially  modified  to  form  a 
support  for  the  head  and  provide  for  its 
movements.  The  head  rests  upon  the 
atlas,  forming  with  it  a  hinge  joint  (used 
in  nodding  to  indicate  "  yes  ");  and  the 
atlas  turns  upon  an  upward  projection 

of  the  axis  forming  a  pivot  joint  (used    pIG  9g_ The  spinal 

in  shaking  the  head  to  indicate  "  no  ").  column. 


V.1 


<Sacrui 


Coccyx. 


224 


MOTION   AND   COORDINATION 


The  next  twelve  vertebrae,  in  order  below  tbe  cervical, 
are  known  as  the  thoracic  vertebrae.  They  form  the  back 
part  of  the  framework  of  the  thorax  and  have  little  free- 
dom of  motion.  The  five  vertebrae  below  the  thoracic  are 
known  as  the  lumbar  vertebrae.  These  bones  are  large 
and  strong  and  admit  of  considerable  motion.  Below  the 
last  lumbar  vertebra  is  a  wedge-shaped  bone  which  has 
the  appearance  of  five  vertebrae  fused  together.  This 
bone,  known  as  the  sacrum,  connects  with  the  large  bones 
which  form  the  pelvic  girdle.  Attached  to  the  lower  end 
of  the  sacrum  is  a  group  of  from  two  to  four  small  verte- 
brae, more  or  less  fused,  called  the  coccyx. 

The  Joining  of  the  Vertebrae.  —  A  typical  vertebra  consists  of  a 
heavy,  disk-shaped  portion  in  front,  called  the  body,  which  is  connected 


FIG.  99.  —  Two  views  of  a  lumbar  vertebra.     A.  From  above.     B.  From 
the  side.     i.  Body.     2,  3, 4,  5.  Projections  from  the  neural  arch. 

with  a  ring-like  portion  behind,  called  the  neural  arch.  The  body  and 
the  neural  arch  together  encircle  a  round  opening  which  is  a  part  of 
the  canal  that  contains  the  spinal  cord  (Fig.  99).  From  the  neural 
arch  are  seven  bony  projections,  or  processes,  three  of  which  serve  for 
the  attachment  of  muscles  and  ligaments,  while  the  other  four,  two 
above  and  two  below,  are  for  the  interlocking  of  the  vertebrae  with 
each  other.  The  separate  vertebrae  are  joined  together  in  the  spinal 
column,  as  follows : 

a.  Between  the  bodies  of  adjacent  vertebrae  are  disks  of  elastic  carti- 
lage.    Each  disk  is  about  one  fourth  of  an  inch  thick  and  is  grown 


THE    SKELETON 


225 


tight  onto  the  face  of  the  vertebra  above  and  also  onto  the  face  of  the 
vertebra  below.  By  means  of  these  disks  a  very  close  connection  is 
secured  between  the  vertebrae  on  the  front  side  of  the  column. 

b.  On  the  back  of  the  column,  the  downward  projections  from  the 
neural  arch  of  each  vertebra  above  fit  into  depressions  found  in  the 
neural  arch  of  the  vertebra  below.     This  interlocking  of  the  vertebras, 
which  is  most  marked  in  the  lumbar  region,  strengthens  greatly  the 
back  portion  of  the  column. 

c.  To  further  secure  one  bone  upon  the  other,  numerous  ligaments 
pass  from  vertebra  to  vertebra  on  all  sides  of  the  column. 

2.  The  Skull.  — The  skull  is  formed  by  the  close  union 
of  twenty-two  irregular  bones.     These  fall  naturally  into 
two  subgroups  —  the  cranium  and  the  face  (Fig.  100).    The 
cranium  consists  of  eight 

thin,  curved  bones  which 
inclose  the  space,  called 
the  cranial  cavity,  that 
holds  the  brain.  The 
face  group,  consisting 
of  fourteen  bones,  pro- 
vides cavities  and  sup- 
ports for  the  different 
organs  of  the  face,  and 
supplies  a  movable  part 
(the  inferior  maxillary)  FIG.  100.— The  skull  (Huxley).  The 

which,    with    the    bones     illustration  shows  most  of  the  bones  of  the 

above   (superior    maxil- 

lary),  forms  the  machine  for  masticating  the  food. 

3.  The  Thorax.  — This  group  contains  twenty-four  bones 
of  similar  form,  called  ribs,  and  a  straight  flat  bone,  called 
the  sternum,  or  breastbone  (Fig.  101).     The  ribs  connect 
with  the  spinal  column  behind,  and  all  but  the  two  lowest 
ones  connect  with  the  sternum  in  front,  and,  by  so  doing, 
inclose  the  thoracic  cavity.     As  already  stated  (page  85), 


Lachr 
mal 


226 


MOTION   AND   COORDINATION 


the  bones  of  the  thorax  form  a  mechanical  device,  or 
machine,  for  breathing.  The  ribs  are  so  arranged  that 
the  volume  of  the  thorax  is  increased  by  elevating  them 
and  diminished  by  depressing  them,  enabling  the  air  to 
be  forced  into  and  out  of  the  lungs. 

4.    The  Shoulder  and  Pelvic  Girdles. — These  groups 
form  two  bony  supports  —  one  at  the  upper  and  the  other  at 

the  lower  portion  of  the 
trunk  —  which  serve  for 
|j.S>  the  attachment  of  the 
arms  and  legs  (Fig.  101). 
The  shoulder  girdle  is 
formed  by  four  bones  — 
two  clavicles,  or  collar 
bones,  and  two  scapulae, 
or  shoulder  blades.  The 
clavicle  on  either  side 
connects  with  the  upper 
end  of  the  sternum  and 
serves  as  a  brace  for  the 
shoulder,  while  the  scap- 
ula forms  a  socket  for  the 
humerus  (the  large  bone 
of  the  arm)  and  supplies 
many  places  for  the  at- 
tachment of  muscles. 

The  pelvic  girdle  con- 
sists of  two  large  bones  of 

irregular  shape,  called  the  innominate  bones.  Tliey  connect 
behind  with  the  sacrum  and  in  front  they  connect,  through 
a  small  pad  of  cartilage,  with  each  other.  On  the  inside  of 
the  girdle  is  a  smooth,  basin-shaped  support  for  the  contents 
of  the  abdomen,  but  on  the  outside  the  bones  are  rough 


Pelvic 
Girdle 


FIG.  101.  —  Bone  groups  of  trunk. 


THE   SKELETON 


227 


and  irregular  and  provide  many  places  for  the  attachment 
of  muscles  and  ligaments.  Each  innominate  bone  has  a 
deep,  round  socket  into  which  the  end  of  the  femur  (the 
long  bone  of  the  leg)  accurately  fits. 

5.  The  Arm  and  PI  and  Groups.  — A  long  bone,  the  hu- 
merus,  connects  the  arm  with  the  shoulder  and  gives  form 
to  the  upper  arm.  In  the  forearm  are  two  bones,  the  radius 
and  the  ulna,  which  connect  at  one  end  with  the  humerus 
and  at  the  other  with  the  bones  of  the  wrist  (Fig.  102). 

A  group  of  eight  small,  round  bones  is  found  in  the 
wrist,  known  as  the  carpal  bones.  These  are  arranged  in 
two  rows  and  are  movable  upon  one  another.  Five  straight 
bones,  the  metacarpals, 
connect  with  the  wrist 
bones  and  form  the 
framework  for  the  palm 
of  the  hand.  Attached 
to  the  metacarpals  are 
the  bones  of  the  fingers 
and  thumb.  These  form 
an  interesting  group  of 
fourteen  bones,  called 
the  phalanges  of  the 
fingers  (Fig.  102). 

The  bones  of  the  hand 
provide  a  mechanical 
device,  or  machine,  for 
grasping,  and  the  arm 
serves  as  a  device  for  moving  this  grasping  machine  from 
place  to  place.  The  work  of  the  arm,  in  this  respect,  is 
not  unlike  that  of  a  revolving  crane  upon  the  end  of  which 
is  a  grab-hook.  The  hand  without  the  arm  to  move  it 
about  would  be  of  little  use. 


Patella 


retatarsus 
SI 

Phalanges 
FIG.  102.  —  Bone  groups  of  arm  and  leg. 


228  MOTION   AND   COORDINATION 

6.  The  Leg  and  Foot  Groups.  —  These  correspond  in  form 
and  arrangement  to  the  bones  of  the  arm  and  hand.  Since, 
however,  the  leg  and  foot  are  used  for  purposes  different 
from  those  of  the  arm  and  hand,  certain  differences  in 
structure  are  to  be  found.  The  patella,  or  kneepan,  has  no 
corresponding  bone  in  the  arm ;  and  the  carpus,  or  ankle, 
which  corresponds  to  the  wrist,  contains  seven  instead  of 
eight  bones.  The  bones  of  the  foot  and  toes  are  the  same 
in  number  as  those  of  the  hand  and  fingers,  but  they  differ 
greatly  in  size  and  form  and  have  less  freedom  of  motion. 
The  femur,  which  gives  form  to  the  thigh,  is  the  longest 
bone  of  the  body.  The  tibia,  or  shin  bone,  and  the  fibula, 
the  slender  bone  by  its  side,  give  form  to  the  lower  part  of 
the  leg  (Fig.  102). 

The  legs  are  mechanical  devices  (walking  machines)  for 
moving  the  body  from  place  to  place.  The  feet  serve  both 
as  supports  for  the  body  and  as  levers  for  pushing  the 
body  forward.  By  their  attachment  to  the  legs  they  may 
be  placed  in  all  necessary  positions  for  supporting  and 
moving  the  body. 

The  different  bone  groups  are  shown  in  Fig.  97  and 
named  in  Table  IV. 

Adaptation  to  Special  Needs.  —  When  any  single  bone  is  studied  in 
its  relation  to  the  other  members  of  the  group  to  which  it  belongs  or 
with  particular  reference  to  its  purpose  in  the  body,  its  adaptation  to 
some  special  place  or  use  is  at  once  apparent.  Each  bone  serves  some 
special  purpose,  and  to  this  purpose  it  is  adapted  by  its  form  and  struc- 
ture. Long  bones,  like  the  humerus  and  femur,  are  suited  to  giving 
strength,  form,  and  stiffness  to  certain  parts,  while  irregular  bones,  like 
the  vertebrae  and  the  pelvic  bones,  are  fitted  for  supporting  and  pro- 
tecting organs.  Others,  like  the  wrist  and  ear  bones,  make  possible  a 
peculiar  kind  of  motion,  and  still  others,  like  the  ribs,  are  adapted  to 
more  than  one  purpose.  The  vast  differences  in  shape,  size,  structure, 
and  surface  among  the  various  bones  are  but  the  conditions  that  adapt 
them  to  particular  forms  of  service  in  the  body. 


THE    SKELETON 


22Q 


TABLE   IV 
THE  PRINCIPAL  BONES  AND  THEIR  GROUPING  IN  THE  BODY 


I.    AXIAL   SKELETON 


A.   Skull,  28. 


1.  Cranium,  8. 

a.  Frontal,  forehead  .  .  .  .  I 

b.  Parietal 2 

c.  Temporal,  temple  ....  2 

d.  Occipital i 

e.  Sphenoid I 

f.  Ethmoid I 

2.  Face,  14. 

a.  Inferior  maxillary  .   .  .  .   I 

b.  Superior  maxillary    ...  2 

c.  Palatine,  palate   .....  2 

d.  Nasal  bones 2 

e.  Vomer i 

f.  Inferior  turbinated    ...  2 

g.  Lachrymal 2 

h.  Malar,  cheek  bones  ...  2 


3.    Bones  of  the  Ears,  6. 

a.  Malleus 2 

b.  Incus 2 

c.  Stapes 2 

B.  Spinal  Column,  26. 

1 .  Cervical,  or  neck,  vertebrae    7 

2.  Dorsal,  or  thoracic,  verte- 

bras    12 

3.  Lumbar  vertebrae 5 

4.  Sacrum i 

5.  Coccyx i 

C.  Thorax,  25. 

1.  Ribs 24 

2.  Sternum i 

D.  Hyoid,  \  (at  base  of  tongue). 


II.    APPENDICULAR   SKELETON 


A.  Shoulder  girdle,  4. 

1.  Clavicle,  collar  bone.  ...  2 

2.  Scapula,  shoulder  blade  .  .  2 

B.  Upper  extremities,  60. 

1.  Humerus 2 

2.  Radius 2 

3.  Ulna 2 

4.  Carpal,  wrist  bones  .  .  .  .  16 

5.  Metacarpal 10 

6.  Phalanges  of  fingers    ...  28 


C.  Pelvic  girdle,  2. 

i.  Os  innominatum 2 

D.  Lmver  extremities,  60. 

1.  Femur,  thigh  bone    ....  2 

2.  Tibia,  shin  bone 2 

3.  Fibula 2 

4.  Patella,  kneepan 2 

5.  Tarsal,  ankle  bones     ...  14 

6.  Metatarsal,  instep  bones    .  10 

7.  Phalanges  of  toes 28 


230  MOTION   AND   COORDINATION 

ARTICULATIONS 

Any  place  in  the  body  where  two  or  more  bones  meet 
is  called  an  articulation,  or  joint  At  the  place  of  meeting 
the  bones  are  firmly  attached  to  each  other,  thereby  secur- 
ing the  necessary  coherence  of  the  skeleton.  The  large 
number  of  bones,  and  consequently  of  articulations,  are 
necessary  for  the  different  movements  of  the  body  and 
also  on  account  of  the  manner  in  which  the  skeleton  de- 
velops, or  grows.  Articulations  are  classed  with  reference 
to  their  freedom  of  motion,  as  movable,  sligJitly  movable, 
and  immovable  articulations. 

Most  of  the  immovable  articulations  are  found  in  the 
skull.  Here  irregular,  tooth-like  projections  from  the  dif- 
ferent bones  enable  them  to  interlock  with  one  another, 
while  they  are  held  firmly  together  by  a  thin  layer  of  con- 
nective tissue.  The  wavy  lines  formed  by  articulations  of 
this  kind  are  called  sutures  (Fig.  100). 

The  best  examples  of  joints  that  are  sligJitly,  but  not 
freely,  movable  are  found  in  the  front  of  the  spinal  column. 
The  cartilaginous  pads  between  the  vertebrae  permit,  by 
their  elasticity,  of  a  slight  bending  of  the  column  in  differ- 
ent directions.  These  movements  are  caused,  not  by  one 
bone  gliding  over  another,  but  by  compressions  and  exten- 
sions of  the  cartilage.  Between  the  vertebrae  in  the  back 
of  the  spinal  column,  however,  there  is  a  slight  movement 
of  the  bone  surfaces  upon  one  another. 

Structure  of  the  Movable  Joints.  —  By  far  the  most  nu- 
merous and  important  of  the  joints  are  those  that  are  freely 
movable.  Such  joints  are  strongly  constructed  and  endure 
great  strain  without  dislocation,  and  yet  their  parts  move 
over  each  other  easily  and  without  friction.  The  ends  of 
the  bones  are  usually  enlarged  and  have  specially  formed 


231 


tella 


projections  or  depressions  which  fit  into  corresponding  de- 
pressions or  elevations  on  the  bones  with  which  they  articu- 
late. In  addition  to  this  the  articular  surfaces  are  quite 
smooth  and  dense,  having  no  Haversian  canals,  and  they 
are  covered  with  a  layer  of  cartilage.  Strong  ligaments 
pass  from  one  bone  to- the  other  to  hold  each  in  its  place 
{A,  Fig.  103).  Some  of  these  consist  simply  of  bands,  con- 
necting the  joint  on  its 
different  sides,  while 
others  form  continuous 
sheaths  around  the  joint. 
The  interior  of  the 
joint,  except  where  the 
bone  surfaces  rub  upon 
each  other,  is  covered 
with  a  serous  lining,  called 
the  synovial  membrane 
(B,  Fig.  103).  This  se- 
cretes a  thick,  viscid  of  nee  jointTendons.  2.  Liga- 
liquid,  the  synovial  fluid,  merits.  3.  Cartilage.  4.  Space  contain- 
which  prevents  friction.  ing  synovial  fluid.  This  space  is  lined, 
~,,  .  ,  i  except  upon  the  articular  surfaces,  by  the 

Ihe  synovial  membrane 

*  synovial  membrane. 

does  not  cover  the  ends 

of  the  bones,  but  passes  around  the  joint  and  connects 
with  the  bones  at  their  edges  so  as  to  form  a  closed  sac 
in  which  the  fluid  is  retained. 

Kinds  of  Movable  Joints.  —  The  different  kinds  of  mova- 
ble joints  are  the  ball  and  socket  joint,  the  hinge  joint,  the 
pivot  joint,  the  condyloid  joint,  and  the  gliding  joint. 
These  are  constructed  and  admit  of  motion,  as  follows: 

i.  In  the  ball  and  socket  joint  the  ball-shaped  end  of 
one  bone  fits  into  a  cup-shaped  cavity  in  another  bone, 
called  the  socket.  The  best  examples  of  such  joints  are 


FIG.  103.  —  Outside  and   inside  view 


232  MOTION   AND   COORDINATION 

found  at  the  hips  and  shoulders.     The  ball  and  socket 
joint  admits  of  motion  in  all  directions. 

2.  In   the   hinge  joint  the  bones  are  grooved  and  fit 
together  after  the  manner  of  a  hinge.     Hinge  joints  are 
found  at  the  elbows  and  knees  and  also  in  the  fingers. 
The  hinge  joint  gives  motion  in  but  two  directions  —  for- 
ward and  backward. 

3.  A  pivot  joint  is  formed  by  the  fitting  of  a  pivot-like 
projection  of  one  bone  into  a  ring-like   receptacle  of  a 
second  bone,  so  that  one,  or  the  other,  is  free  to  turn. 
A  good  example  of  the  pivot  joint  is  found  at  the  elbow, 
where  the  radius  turns  upon  the  humerus.     Another  ex- 
ample is  the  articulation  of  the  atlas  with  the  axis  vertebra 
as  already  noted.     The  pivot  joint  admits  of  motion  around 
an  axis. 

4.  The  condyloid  joint  is  formed  by  the  fitting  of  the 
ovoid  (egg-shaped)  end  of  one  bone  into  an  elliptical  cavity 
of  a  second  bone.     Examples  of  condyloid  joints  are  found 
at  the  knuckles  and  where  the  wrist  bones  articulate  with 
the  radius  and  ulna.     They  move  easily  in  two  directions, 
like  hinge  joints,  and  slightly  in  other  directions. 

5.  Gliding  joints  are  formed  by  the  articulation  of  plain 
(almost   flat)   surfaces.     Examples   of   gliding  joints    are 
found  in  the  articulations  between  the  bones  of  the  wrist 
and   those  of  the  ankle.     They  are  the  simplest  of  the 
movable  joints  and  are  formed  by  one  bone  gliding,  or  slip- 
ping, upon  the  surface  of  another. 

The  Machinery  of  the  Body.  —  A  machine  is  a  contrivance  for  direct- 
ing energy  in  doing  work.  A  sewing  machine,  for  example,  so  directs 
the  energy  of  the  foot  that  it  is  made  to  sew.  Through  its  construction 
the  machine  is  able  to  produce  just  that  form  of  motion  needed  for 
its  work,  and  no  other  forms,  so  lhat  energy  is  not  wasted  in  the  pro- 
duction of  useless  motion.  The  places  in  machines  where  parts  rub  or 


THE    SKELETON  233 

turn  upon  each  other  are  called  bearings,  and  extra  precautions  are  taken 
in  the  construction  and  care  of  the  bearings  to  prevent  friction. 

The  body  cannot  properly  be  compared  to  any  single  machine,  but 
must  be  looked  upon  as  a  complex  organization  which  employs  a  num- 
ber of  different  kinds  of  machines  in  carrying  on  its  work.  The  major- 
ity of  these  machines  are  found  in  the  skeleton.  The  bones  are  the 
parts  that  are  moved,  and  the  joints  serve  as  bearings.  Connected 
with  the  bones  are  the  muscles  that  supply  energy,  and  attached  to 
the  muscles  are  the  nerves  that  control  the  motion.  Other  parts  also 
are  required  for  rendering  the  machines  of  the  body  effective  in  doing 
work.  These  are  supplied  by  the  tissues  connected  with* the  bones 
and  the  muscles. 


HYGIENE   OF  THE   SKELETON 

Of  chief  concern  in  the  hygiene  of  the  skeleton  is  the 
proper  adjustment  of  its  parts.  The  efficiency  of  any  of 
the  body  machines  is  impaired  by  lack  of  proper  adjust- 
ment. Not  only  this,  but  because  of  the  fact  that  the  skele- 
ton forms  the  groundwork  of  the  whole  body  —  muscles, 
blood  vessels,  nerves,  everything  in  fact,  being  arranged 
with  reference  to  it —  any  lack  of  proper  adjustment  of  the 
bones  interferes  generally  with  the  arrangement  and  work 
of  tissues  and  organs.  The  displaced  bones  may  even 
compress  blood  vessels  and  nerves  and  interfere,  in  this 
way,  with  the  nourishment  and  control  of  organs  remote 
from  the  places  where  the  displacements  occur.  For  these 
reasons  the  proper  adjustment  of  the  different  parts  of  the 
skeleton  supplies  one  of  the  essential  conditions  for  pre- 
serving the  health. 

Hygienic  Importance  of  the  Spinal  Column.  —  What  has 
been  said  about  the  adjustment  of  the  skeleton  in  general 
applies  with  particular  force  to  the  spinal  column.  The 
spinal  column  serves  both  as  the  central  axis  of  the  body 
and  as  the  container  of  the  spinal  cord.  Thirty-one  pairs 


234 


MOTION   AND   COORDINATION 


FIG.    104.  —  A    tendency 

toward    spinal   curvature    (after 
Mosher). 


of  nerves  pass  between  the  ver- 
tebrae to  connect  the  spinal  cord 
with  different  parts  of  the  body, 
and  two  important  arteries  (the 
vertebral)  pass  through  a  series 
of  small  openings  in  the  bones 
of  the  neck  to  reach  the  brain. 
Unnatural  curves  of  the  spine 
throw  different  parts  of  the  body 
out  of  their  natural  positions, 
diminish  the  thoracic  and  abdom- 
inal cavities,  and,  according  to 
the  belief  of  certain  physicians, 

compress  the  nerves  that  pass  from  the  cord  to  other  parts 

of  the  body.     Slightly  misplaced  vertebrae  in  the  neck,  by 

compressing  the  vertebral 

arteries,  may  also  interfere 

with  the  supply  of  blood 

to  the  brain. 

How  the  Skeleton  becomes 

Deformed.  — We  are  accus- 
tomed   to    look   upon   the 

skeleton  as  a  rigid  frame- 
work   which  can    get   out 

of    its    natural    form  only 

through  severe  strain  or  by 

violence.      This  view  is  far 

from   being    correct.      On 

account  of  their  necessary 

freedom    of     motion,    the 

bones,  especially  those  of 


FIG.  105.  —  Effect  on  spinal  column 

of  improper  position  in  writing.     (  From 
Pyle's  Personal  Hygiene,") 


the    spinal  column,   are  easily  slipped  from  their  normal 
positions;  and   where    improper    attitudes    are   frequently 


THE   SKELETON  235 

assumed,  or  continued  through  long  periods  of  time,  the 
skeleton  gradually  becomes  deformed  (Fig.  104).  For  ex- 
ample, the  habit  of  always  sleeping  on  the  same  side  with  a 
high  pillow  may  develop  a  bad  crook  in  the  neck;  and  the 
ugly  curves,  assumed  so  frequently  in  writing1  (Fig.  105), 
and  also  in  standing,  when  the  weight  is  shifted  too 
much  on  one  foot,  may  become  permanent.  Then  the 
habit  of  reclining  in  a  chair  with  the  hips  resting  on  the 
front  of  the  seat  often  deforms  the  back  and  causes  a 
drooping  of  the  shoulders.  In  fact,  slight  displacements 
of  the  vertebrae  come  about  so  easily  through  incorrect 
positions,  that  they  may  almost  be  said  to  "  occur  of  them- 
selves "  where  active  measures  are  not  taken  to  preserve 
the  natural  form  of  the  body.  The  very  few  people  who 
have  perfectly  formed  bodies  show  to  what  an  extent  has 
been  overlooked  an  essential  law  of  hygiene. 

Prevention  of  Skeletal  Deformities.  —  Those  deformities 
of  the  skeleton  that  are  acquired  through  improper  posi- 
tions are  prevented  by  giving  sufficient  attention  to  the 
positions  assumed  in  sitting,  standing,  and  sleeping,  and 
also  to  the  posture  in  various  kinds  of  work.  In  sitting 
the  trunk  should  be  erect  and  the  hips  should  touch  the 
back  of  the  chair.  One  should  not  lounge  in  the  ordinary 
chair.  In  standing  the  body  should  be  erect,  the  shoulders 
back  and  down,  the  chest  pushed  slightly  up  and  forward, 
and  the  chin  slightly  depressed,  while  the  weight  should, 
as  a  rule,  rest  about  equally  on  the  two  feet.  The  habit  of 
leaning  against  some  object  when  standing  (the  pupil  in 


1  It  has  been  claimed  that  the  introduction  of  vertical  writing  has  reduced  the 
number  of  cases  of  spinal  curvature  originating  in  the  schoolroom,  and  statistics 
appear  to  prove  the  claim.  It  is  shown,  on  the  other  hand,  that  unnatural  positions 
also  are  unnecessary  in  the  slanting  system  of  writing,  and  that  in  either  system  the 
pupil  who  is  permitted  to  do  so  is  liable  to  assume  an  improper  position. 


236  MOTION   AND   COORDINATION 

reciting  often  leans  on  his  desk)  should  be  avoided.  In 
sleeping  the  pillow  should  be  of  the  right  thickness  to  sup- 
port the  head  on  a  level  with  the  spinal  column  and  should 
not  be  too  soft.  If  one  sleeps  on  his  back,  no  pillow  is 
required.  It  is  best  not  to  acquire  the  habit  of  sleeping 
always  on  the  same  side. 

Where  one  is  compelled  by  his  work  to  assume  harmful 
positions,  these  should  be  corrected  by  proper  exercises, 
and  by  cultivating  opposing  positions  during  the  leisure 
hours.  Much  is  to  be  accomplished  through  those  forms 
of  physical  exercise  which  develop  the  muscles  whose 
work  it  is  to  keep  the  body  in  an  upright  position. 

School  Furniture.  —  It  has  long  been  observed  that  school  children 
are  more  subject  to  curvature  of  the  spine  and  other  deformities  of  the 
skeleton  than  the  children  who  do  not  attend  school.     While  this  is 
due  largely  to  faulty  positions  assumed  by  the  pupils  at  their  work,  it 
has  been  suggested  that  the  school  furniture 
may  be  in  part  to  blame  for  these  positions. 
Investigations  of  this  problem  have  shown  that 
most  of  the  school  desks  and  seats  in  use  in 
our   public   schools    are    unhygienically   con- 
structed, in  that  they  force  pupils  into  unnatural 
positions.     School    seats   should    support  the 
pupil  in  a  natural  position,  both  in  the  use  of 
his  books  and  in  writing,  and  there  are  many 
arguments  in  favor  of  the  so-called  "adjustable" 
school  furniture.     Fig.  106  shows  the  seat  and 
FIG.     106.  —  Adjust-    (^es'<  designed  by  the  Boston,  Mass.,  School- 
able seat  and  desk  used    house  Commission  after  much  study  and  experi- 
in    schools    of    Boston,   meriting  and  used  in  the  Boston  schools.     This 
Mass.  furniture,  which  provides  a  seat  adjustable  for 

height,  having  a  back  rest  also  adjustable  for 

height,  and  a  desk  which  is  likewise  provided  with  a  vertical  adjustment, 
supplies  all  essential  hygienic  requirements.  It  is  to  be  hoped  that 
school  furniture  of  this  character  may  in  the  near  future  come  into 
general  use. 


THE    SKELETON  237 

Correction  of  Skeletal  Deformities. —  It  is,  of  course,  easier 
to  prevent  deformities  of  the  skeleton  by  giving  attention 
to  proper  positions,  than  to  correct  them  after  they  have 
occurred.  It  should  also  be  noted  that  severe  deformities 
cannot  be  corrected  by  the  individual  for  himself,  but  these 
must  come  under  the  treatment  of  specialists  in  this  line 
of  medical  work.  In  mild  cases  of  spinal  curvature,  droop- 
ing of  the  head,  and  round  shoulders,  the  individual  can 
benefit  his  condition.  By  working  to  "  substitute  a  correct 
attitude  for  the  faulty  one,"  J  he  can  by  persistence  bring 
about  marked  improvements.  It  is  better,  however,  to 
have  the  advice  and  aid  of  a  physical  director,  where  this 
is  possible.  It  should  also  be  borne  in  mind  that  the  cor- 
rection of  skeletal  deformities  requires  effort  through  a 
long  period  of  time,  especially  where  the  deformities  are 
pronounced;  and  one  lacking  the  will  power  to  persist  will 
not  secure  all  the  results  which  he  seeks. 

"  Setting  Up"  Exercises.  —  The  splendid  carriage  of  students  from 
military  schools  shows  what  may  be  accomplished  in  securing  erectness 
of  form  where  proper  attention  is  given  to  this  matter.  The  military 
student  gets  his  fine  form  partly  through  his  exercises  in  handling  arms, 
but  mainly  through  his  so-called  "setting  up"  drill.  As  a  suggestion 
to  one  desiring  to  improve  the  form  of  his  body,  a  modification  of  the 
usual  setting  up  drill  is  here  given : 

1.  Standing  erect,  with  the  heels  together,  the  feet  at  an  angle  of  45°, 
and  hands  at  the  sides,  bring  the  arms  to  a  horizontal  position  in  front, 
little  fingers  touching  and  nails  down.     From  this  position  raise  the 
hands  straight  over  the  head,  bringing  the  palms  gradually  together. 
Then  with  a  backward  sweeping  movement,  return  the  hands  again  to 
the  sides.     Repeat  several  times. 

2.  With  the  feet  as  in  the  above  exercise,  bring  the  hands  and  the 
arms  to  a  level  with  the  shoulders,  palms  down,  elbows  bent,  middle 
fingers  of  the  two  hands  touching,  and  the  extended  thumbs  touching 
the  chest.     Keeping  the  palms  down  and  the  arms  on  a  level  with  the 

l  Lovett,  Lateral  Curvature  of  the  Spine  and  Round  Shoulders. 


238  MOTION    AND    COORDINATION 

shoulders,  extend  the  hands  as  far  sideward  and  backward  as  possible, 
returning  each  time  to  the  first  position.  As  the  hands  move  out,  in- 
hale deeply  (through  the  nose),  and  as  they  are  brought  back,  exhale 
quickly  (through  the  mouth).  Repeat  several  times. 

3.  With  the  arms  at  the  sides  and  the  feet  side  by  side  and  touching, 
bring  the  hands  in  a  circular  movement  to  a  vertical  position  over  the 
head,  and  lock  the  thumbs.  Keeping  the  knees  straight  and  the  thumbs 
locked,  bend  forward,  letting  the  hands  touch  the  ground  if  possible, 
and  then  bring  the  body  and  hands  again  to  the  vertical  position. 
Then  by  a  backward  sweeping  movement,  return  the  hands  again  to 
the  sides.  Repeat. 

While  these  exercises  may  be  practiced  whenever  convenient,  it  is 
best  to  set  apart  some  special  time  each  day  for  them,  as  on  retiring  at 
night  or  on  rising  in  the  morning. 

Hygienic  Footwear.  —  A  necessary  aid  to  erectness  of 
position  in  standing  and  walking  is  a  properly  fitting  shoe. 
Heels  that  are  too  high  tilt  the  body  unnaturally  forward, 
and  shoes  that  cause  any  kind  of  discomfort  in  walking 
lead  to  unnatural  positions  in  order  to 
protect  the  feet.  Shoes  should  fit 
snugly,  being  neither  too  large  nor 
too  small.  Many  shoes,  however,  are 

unhygienically    constructed,    and     no 
Fi<;.  107.  —  Heels  and  ,        ,  ,  , 

toes  of  unhygienic  and  attempt  should  be  made  to  wear  them, 
of  hygienic  footwear.  Certainly  is  this  true  of  styles  that 

approach  the  "French  heel"  or  the 
"toothpick  toe"  (Fig.  107).  However,  many  styles  of 
shoes  are  manufactured  that  are  both  hygienic  and  neat 
fitting.  Rubber  heels,  on  account  of  their  elasticity,  are 
to  be  preferred  to  those  made  of  leather. 

The  Skeleton  in  Childhood  and  Old  Age.  —  Certain  pecul- 
iarities are  found  to  exist  in  the  bones  of  children  and  of 
old  people  which  call  for  special  care  of  the  skeleton  during 
the  first  and  last  periods  of  life.  The  bones  of  children  are 
soft,  lacking  mineral  matter,  and  are  liable  to  become  bent 


THE    SKELETON  239 

For  this  reason,  children  who  are  encouraged  to  walk  at 
too  early  an  age  may  bend  the  thigh  bones,  causing  the 
too  familiar  "bow-legs."  These  bones  may  also  be  bent 
by  having  children  sit  on  benches  and  chairs  which  are  too 
high  for  the  feet  to  reach  the  floor,  and  which  do  not  pro- 
vide supports  for  the  feet.  Wholesome  food,  fresh  air, 
sunlight,  and  exercise  are  also  necessary  to  the  proper  de- 
velopment of  the  bones  of  children.  Where  these  natural 
conditions  are  lacking,  as  in  the  crowded  districts  of  cities, 
children  often  suffer  from  a  disease  known  as  "  rickets," 
on  account  of  which  their  bones  are  unnaturally  soft  and 
easily  bent. 

On  account  of  the  accumulation  of  mineral  matter,  the 
bones  of  elderly  people  become  brittle  and  are  easily 
broken,  and  from  lack  of  vigor  of  the  bone  cells  they  heal 
slowly  after  such  injuries  occur.  This  makes  the  breaking 
of  a  bone  by  an  aged  person  a  serious  matter.  Old  people 
should,  as  far  as  possible,  avoid  liabilities  to  falls,  such  as 
going  rapidly  up  and  down  stairs,  or  walking  on  icy  side- 
walks, and  should  use  the  utmost  care  in  getting  about.  In 
old  people  also  the  cartilage  between  the  bones  softens, 
increasing  the  liability  of  getting  misshaped.  Special  atten- 
tion, therefore,  should  be  given  to  erectness  of  form,  and 
to  such  exercises  as  tend  to  preserve  the  natural  shape  of 
the  body. 

Treatment  of  Fractures.  —  A  fractured  bone  always  re- 
quires the  aid  of  a  surgeon,  and  no  time  should  be  lost  in 
securing  his  services.  In  the  meantime  the  patient  should  be 
put  in  a  comfortable  position,  and  the  broken  limb  supported 
above  the  rest  of  the  body.  Though  the  breaking  of  a 
bone  is  not,  as  a  rule,  a  serious  mishap,  it  is  necessary  that 
the  very  best  skill  be  employed  in  setting  it.  Any  failure 
to  bring  the  ends  of  the  broken  bone  into  their  normal 


240  MOTION    AND   COORDINATION 

relations  permanently  deforms  the  limb  and  interferes  with 
its  use. 

Dislocations  and  Sprains.  —  Dislocations,  if  they  be  of  the 
larger  joints,  also  require  the  aid  of  the  surgeon  in  their 
reduction  and  sometimes  in  their  subsequent  treatment. 
Simple  dislocations  of  the  finger  joints,  however,  may  be 
reduced  by  pulling  the  parts  until  the  bones  can  be  slipped 
into  position. 

A  sprain,  which  is  an  overstrained  condition  of  the  liga- 
ments surrounding  a  joint,  frequently  requires  very  careful 
treatment.  When  the  sprain  is  at  all  serious,  a  physician 
should  be  called.  Because  of  the  limited  supply  of  blood 
to  the  ligaments,  they  are  slow  to  heal,  and  the  temptation 
to  use  the  joint  before  it  is  fully  recovered  is  always  great. 
Massage  1  judiciously  applied  to  a  sprained  joint,  by  bring- 
ing about  a  more  rapid  change  in  the  blood  and  the  lymph, 
is  beneficial  both  in  relieving  the  pain,  and  in  hastening 
recovery. 

Summary.  —  The  skeleton,  or  framework  of  the  body, 
is  a  structure  which  is  movable  as  a  whole  and  in  most  of 
its  parts.  It  preserves  the  form  of  the  body,  protects 
important  organs,  and  supplies  the  mechanical  devices,  or 
machines,  upon  which  the  muscles  act  in  the  production 
of  motion.  The  skeleton  is  adapted  to  its  purposes 
through  the  number  and  properties  of  the  bones,  and 
through  the  cartilage  and  connective  tissue  associated 
with  the  bones.  The  places  where  the  different  bones 
connect  one  with  another  are  known  as  joints,  and  most 
of  these  admit  of  motion.  The  preservation  of  the  natural 
form  of  the  skeleton  is  necessary,  both  for  its  proper  action 
and  for  the  health  of  the  body. 

1  See  "  Hygiene  of  Muscles,"  Chapter  XV. 


THE    SKELETON  341 

Exercises.  —  i.  State  the  main  purpose  of  the  skeleton.  What  is  the 
necessity  for  so  many  bones  in  its  construction? 

2.  How  may  the  per  cent  of  animal  and  of  mineral  matter  in  a  bone 
be  determined? 

3.  What   properties  are  given  the  bones  by  the  animal   matter? 
What  by  the  mineral  matter? 

4.  Locate  the  bone  cells.     What  is  their  special  function? 

5.  State  the  plan  by  which  nourishment  is  supplied  to  the  bone  cells 
in  different  parts  of  the  bone. 

6.  Give  the  uses  of  the  periosteum. 

7.  State  the  purpose  of  the  Haversian  canals.     Of  the  canaliculi. 

8.  Give  functions  of  the  spinal  column. 

9.  Name  the  different  materials  used  in  the  construction  of  a  joint 
and  the  purpose  served  by  each. 

10.  Name  four  mechanical  devices,  or  machines,  found  in  the  skele- 
ton and  state  the  purpose  served  by  each. 

11.  Name  one  or  more  of  the  body  machines  not  located  in  the 
skeleton. 

12.  Of  what  advantage  is  the  peculiar  shape  of  the  lower  jaw?     Of 
the  ribs?     Of  the  bones  of  the  pelvic  girdle? 

13.  State   the   importance    of  preserving  the   natural    form  of  the 
skeleton.     How  are  unnatural  curves  produced  in  the  spinal  column? 

14.  How  may  slight  deformities  of  the  skeleton  be  corrected? 

15.  What  different  systems  are  employed  in  the  body  in  the  produc- 
tion of  motion?     What  is  the  special  function  of  each? 

PRACTICAL  WORK 

To  obtain  clear  ideas  of  the  form  and  functions  of  the  bones,  a 
careful  examination  of  a  prepared  and  mounted  skeleton  is  necessary. 
Many  of  the  bones,  however,  may  be  located  and  their  general  form 
made  out  from  the  living  body.  Bones  of  the  lower  animals  may  also 
be  studied  to  advantage. 

Experiments  to  show  the  Composition  of  Bone.  —  i .  Examine  a 
slender  bone,  like  that  in  a  chicken's  leg.  Note  that  it  resists  bending 
and  is  difficult  to  break.  Note  also  that  it  is  elastic  —  that,  when  slightly 
bent,  it  will  spring  back. 

2.  Soak  such  a  bone  over  night  in  a  mixture  of  one  part  hydrochloric 
acid  and  four  parts  water.  Then  ascertain  by  bending,  stretching,  and 


242  MOTION    AND   COORDINATION 

twisting  what  properties  the  bone  has  lost.  The  acid  has  dissolved  out 
the  mineral  matter. 

3.  Burn  a  small  piece  of  bone  in  a  clear  gas  flame,  or  on  a  bed  of 
coals,  until  it  ceases  to  blaze  and  turns  a  white  color.  Can  the  bone 
now  be  bent  or  twisted  ?  What  properties  has  it  lost  and  what  retained  ? 
What  substance  has  been  removed  from  the  bone  by  burning? 

Observation  on  the  Gross  Structure  of  Bone.  —  i.  Procure  a  long, 
dry  bone.  (One  that  has  lain  out  in  the  field  until  it  has  bleached 
will  answer  the  purpose  excellently.)  Test  its  hardness,  strength,  and 
stiffness.  Saw  it  in  two  a  third  of  the  distance  from  one  end.  and  saw 
the  shorter  piece  in  two  lengthwise.  Compare  the  structure  at  different 
places.  Find  rough  elevations  on  the  outside  for  the  attachment  of 
muscles,  and  small  openings  into  the  bone  for  the  entrance  of  blood 
vessels  and  nerves.  Make  drawings  to  represent  the  sections. 

2.  Procure  a  fresh  bone  from  the  butcher  shop.  Note  the  difference 
between  it  and  the  dry  bone.  Examine  the  materials  surrounding  the 
sides  and  covering  the  ends  of  the  bone.  Saw  through  the  enlarged 
portion  at  the  end  and  examine  the  red  marrow.  Saw  through  the 
middle  of  the  bone  and  observe  the  yellow  marrow. 

To  show  the  Minute  Structure  of  the  Bone. — Prepare  a  section  of 
bone  for  microscopic  study  as  follows :  With  a  jeweler's  saw  cut  as 
thin  a  slice  as  possible.  Place  this  upon  a  good-sized  whetstone,  not 
having  too  much  grit,  and  keeping  it  wet  rub  it  under  the  finger,  or  a 
piece  of  leather,  until  it  is  thin  enough  to  let  the  light  shine  through. 
The  section  may  then  be  washed  and  examined  with  the  microscope.  If 
the  specimen  is  to  be  preserved  for  future  study,  it  may  be  mounted  in 
the  usual  way,  but  with  hard  balsam.  Prepare  and  study  both  trans- 
verse and  longitudinal  sections,  making  drawings.  The  sections  should 
be  prepared  from  bones  that  are  thoroughly  dry  but  which  have  not 
begun  to  decay. 

To  show  the  Structure  of  a  Joint.  —  Procure  from  a  butcher  the  joint 
of  some  small  animal  (hog  or  sheep).  Cut  it  open  and  locate  the  carti- 
lage, synovial  membrane,  and  ligaments.  Observe  the  shape  and  surface 
of  the  rubbing  parts  and  the  strength  of  the  ligaments. 


CHAPTER   XV 
THE  MUSCULAR  SYSTEM 

As  already  stated,  the  skeleton,  the  nervous  system,  and 
the  muscular  system  are  concerned  in  the  production  of 
motion.  The  skeleton  and  the  nervous  system,  however, 
serve  other  purposes  in  the  body,  while  the  muscular  sys- 
tem is  devoted  exclusively  to  the  production  of  motion. 
For  this  reason  it  is  looked  upon  as  the  special  motor  sys- 
tem. The  muscular  tissue  is  the  most  abundant  of  all  the 
tissues,  forming  about  41  per  cent  of  the  weight  of  the  body. 

Properties  of  Muscles.  —  The  ability  of  muscular  tissue 
to  produce  motion  depends  primarily  upon  two  proper- 
ties —  the  property  of  irritability  and  the  property  of 
contractility.  Irritability  is  that  property  of  a  substance 
which  enables  it  to  respond  to  a  stimulus,  or  to  act  when 
acted  upon.  Contractility  is  the  property  which  enables 
the  muscle  when  stimulated  to  draw  up,  thereby  becoming 
shorter  and  thicker  (a  condition  called  contraction),  and 
when  the  stimulation  ceases,  to  return  to  its  former  condi- 
tion (of  relaxation).  The  property  of  contractility  enables 
the  muscles  to  produce  motion.  Irritability  is  a  condition 
necessary  to  their  control  in  the  body. 

Kinds  of  Muscular  Tissue.  —  Three  kinds  of  muscular 
tissue  are  found  in  the  body.  These  are  known  as  the 
striated,  or  striped,  muscular  tissue ;  the  non-striated,  or 
plain,  muscular  tissue ;  and  the  muscular  tissue  of  the 
heart.  These  are  made  up  of  different  kinds  of  muscle 
cells  and  act  in  different  ways  to  cause  motion.  The 

243 


244 


MOTION    AND    COORDINATION 


striated  muscular  tissue  far  exceeds  the  others  in  amount 
and  forms  all  those  muscles  that  can  be  felt  from  the  sur- 
face of  the  body.  The  non-striated  muscle  is  found  in  the 
walls  of  the  food  canal,  blood  vessels,  air  passages,  and 
other  tubes  of  the  body ;  while  the  muscular  tissue  of  the 
heart  is  confined  entirely  to  that  organ. 

Striated  Muscle  Cells.  —  The  cells  of  the  striated  mus- 
cles are  slender,  thread-like  structures,  having  an  average 
length  of  i|  inches  (35  millimeters)  and 
a  diameter  of  about  -%^-Q  of  an  inch  (60  /*). 
Because  of  their  great  length  they  are 
called  fibers,  or  fiber  cells.  They  are 
marked  by  a  number  of  dark,  transverse 
bands,  or  stripes,  called  striations,1  which 
seem  to  divide  them  into  a  number  of  sec- 
tions, or  disks  (Fig.  108).  A  thin  sac-like 
covering,  called  the  sarcolemma^  surrounds 
the  entire  cell  and  just  beneath  this  are  a 
number  of  nuclei.2 

Within  the  sarcolemma  are  minute  fibrils 
and  a  semiliquid  substance,  called  the  sar- 

°  '  ~~,     coplasm.     At  each  end  the  cell  tapers  to  a 
striated     muscle       r-t 

cell  highly  magni-  point  from  which  the  sarcolemma  appears 
fied,  showing  stria-  to  continue  as  a  fine  thread,  and  this,  by 
tions  and  nuclei,  attaching  itself  to  the  inclosing  sheath, 

Attached  to  the  cell    ,1-1^1  ,,  .         ,  , ,  r    , 

is  the  termination  holds  the  cell  in  place.  Most  of  the  muscle 
of  a  nerve  fiber.  ce^s  receive,  at  some  portion  of  their  length, 
the  termination  of  a  nerve  fiber.  This 
penetrates  the  sarcolemma  and  spreads  out  upon  a  kind  of 
disk,  having  several  nuclei,  known  as  the  end  plate. 

1  On  account  of  the  striations  of  these  cells  the  muscles  which  they  form  are 
called  striated  muscles. 

2  The  striated  muscle  cells,  having  many  nuclei,  are  said  to  be  multi-nucleated. 


THE    MUSCULAR    SYSTEM 


245 


FIG.  109.  —  Diagram 
of  a  section  of  a  muscle, 


The  "Muscle-organ."  — We  must  dis- 
tinguish between  the  term  "  muscle  " 
as  applied  to  the  muscular  tissue  and 
the  term  as  applied  to  a  working  group 
of  muscular  tissue,  which  is  an  organ. 
In  the  muscle,  or  muscle-organ,  is 
found  a  definite  grouping  of  muscle 
fibers  such  as  will  enable  a  large  num- 
ber of  them  to  act  together  in  the  pro-  showing  the  perimysium 

duction  of  the  same  movement.     An    and  the  bundles  of  fiber 

examination    of    one    of    the    striated 

muscles  shows  the  individual  fibers  to  lie  parallel  in  small 

bundles,  each  bundle  being  surrounded  by  a  thin  layer  of 

connective   tissue.      (See    Practical  Work.)     These  small 

bundles  are  bound  into  larger 
ones  by  thicker  sheaths  and 
these  in  turn  may  be  bound 
into  bundles  of  still  larger 
size  (Fig.  109).  The  sheaths 
surrounding  the  fiber  bun- 
dles are  connected  with  one 
another  and  also  with  the 
outer  covering  of  the  mus- 
cle, known  as 

The  Perimysium.  —  The 
plan  of  the  muscle-organ  is 
revealed  through  a  study  of 
the  perimysium.  This  is  not 
limited  to  the  surface  of  the 
FIG.  no. —  A  muscle-organ  in  muscle,  as  the  name  sug- 

position.     The  tendons  connect  at  one  but   properly  includes 

end  with  the  bones  and  at  the  other    c 

end  with  the  fiber  cells  and  perimysium.    the  sheaths  that  surround  the 

(See  text.)  bundles  of  fibers.     Further- 


.TENDONS 


ARTERY 


VEIN 


246  MOTION    AND   COORDINATION 

more,  the  surface  perimysium  and  that  within  the  muscle 
are  both  continuous  with  the  strong,  white  cords,  called 
tendons,  that  connect  the  muscles  with  the  bones.  By 
uniting  with  the  bone  at  one  end  and  blending  with  the 
perimysium  and  fiber  bundles  at  the  other,  the  tendon 
forms  a  very  secure  attachment  for  the  muscle.  The 
perimysium  and  the  tendon  are  thus  the  means  through 
which  the  fiber  cells  in  any  muscle-organ  are  made  to  pull 
together  upon  the  same  part  of  the  body  (Fig.  1 10). 

Purpose  of  Striated  Muscles.  —  The  striated  muscles, 
by  their  attachments  to  the  bones,  supply  motion  to  all  the 
mechanical  devices,  or  machines,  located  in  the  skeleton. 
Through  them  the  body  is  moved  from  place  to  place  and 
all  the  external  organs  are  supplied  with  such  motion  as 
they  require.  Because  of  the  attachment  of  the  striated 
muscles  to  the  skeleton,  and  their  action  upon  it,  they  are 
called  skeletal  muscles.  As  most  of  them  are  under  the 
control  of  the  will,  they  are  also  called  voluntary  muscles. 
They  are  of  special  value  in  adapting  the  body  to  its  sur- 
roundings. 

Structure  of  the  Non-striated  Muscles. — The  cells  of 
the  non-striated  muscles  differ  from  those  of  the  striated 
muscles  in  being  decidedly  spindle-shaped  and  in  having 
but  a  single  well-defined  nucleus  (Fig.  1 1 1).  Furthermore, 
they  have  no  striations,  and  their  connection  with  the  nerve 
fibers  is  less  marked.  They  are  also  much  smaller  than  the 
striated  cells,  being  less  than  one  one-hundredth  of  an  inch 
in  length  and  one  three-thousandth  of  an  inch  in  diameter. 

In  the  formation  of  the  non-striated  muscles,  the  cells 
are  attached  to  one  another  by  a  kind  of  muscle  cement  to 
form  thin  sheets  or  slender  bundles.  These  differ  from 
the  striated  muscles  in  several  particulars.  They  are  of  a 
pale,  whitish  color,  and  they  have  no  tendons.  Instead  of 


THE    MUSCULAR    SYSTEM 


24; 


being  attached  to  the  bones,  they  usually  form  a  distinct 
layer  in  the  walls  of  small  cavities  or  of  tubes  (Fig.  in). 
Since  they  are  controlled  by  the 
part  of  the  nervous  system  which 
acts  independently  of  the  will, 
they  are  said  to  be  involuntary. 
They  contract  and  relax  slowly. 
Work  of  the  Non-striated  Mus- 
cles. —  The  work  of  the  non- 
striated  muscles,  both  in  purpose 
and  in  method,  is  radically  dif- 
ferent from  that  of  the  striated. 
„,,  ,  .  .  FIG.  in.  —  Non-striated 

They  do  not  change  the  position  muscle  cells.  A.  Cross  section 
of  parts  of  the  body,  as  do  the  of  small  artery  magnified,  show- 
striated  muscles,  but  they  alter  ins  CO  the  Ia7er  of  non-striated 
the  sise  and  shape  of  the  parts  cells'  B'  Three  non-striated 

f  cells  highly  magnified. 

which  they  surround.  Their  pur- 
pose, as  a  rule,  is  to  move,  or  control  the  movement  of, 
materials  within  cavities  and  tubes,  and  they  do  this  by 
means  of  the  pressure  which  they  exert.  Examples  of  their 
action  have  already  been  studied  in  the  propulsion  of  the 
food  through  the  alimentary  canal  and  in  the  regulation  of 
the  flow  of  blood  through  the  arteries  (pages  159  and  49). 
While  they  do  not  contract  so  quickly,  nor  with  such  great 
force  as  the  striated  muscles,  their  work  is  more  closely 
related  to  the  vital  processes. 

Structure  of  the  Heart  Muscle. — The  cells  of  the  heart 
combine  the  structure  and  properties  of  the  striated  and  the 
non-striated  muscle  cells,  and  form  an  intermediate  type  be- 
tween the  two.  They  are  cross-striped  like  the  striated  cells, 
and  are  nearly  as  wide,  but  are  rather  short  (Fig.  112). 
Each  cell  has  a  well-defined  nucleus,  but  the  sarcolemma  is 
absent.  They  are  placed  end  to  end  to  form  fibers,  and 


24$  MOTION   AND   COORDINATION 

many  of  the  cells  have  branches  by  which  they  are  united 
to  the  cells  in  neighboring  fibers.  In  this  way  they  inter- 
lace more  or  less  with  each  other,  but 
are  also  cemented  together.  They  con- 
tract quickly  and  with  great  force,  but  are 
not  under  control  of  the  will.  Muscular 
tissue  of  this  variety  seems  excellently 


m 


adapted  to  the  work  of  the  heart. 

The     Muscular     Stimulus.  —  The    in- 
FIG.  112.  —  Muscle 

cells  from  the  heart,  active,  or  resting,  condition  of  a  muscle 
highly  magnified  (after  js  that  of  relaxation.  It  does  work 
Schafer).  through  contracting.  It  becomes  active, 

or  contracts,  only  when  it  is  being  acted  upon  by  some  force 
outside  of  itself,  and  it  relaxes  again  when  this  force  is  with- 
drawn. Any  kind  of  force  which,  by  acting  on  muscles, 
causes  them  to  contract,  is  called  a  muscular  stimulus. 
Electricity,  chemicals  of  different  kinds,  and  mechanical 
force  may  be  so  applied  to  the  muscles  as  to  cause  them  to 
contract.  These  are  artificial  stimuli.  So  far  as  known, 
muscles  are  stimulated  naturally  in  but  one  way.  This 
is  through  the  nervous  system.  The  nervous  system  sup- 
plies a  stimulus  called  the  nervous  impulse,  which  reaches 
the  muscles  by  the  nerves,  causing  them  to  contract.  By 
means  of  nervous  impulses,  all  of  the  muscles  (both  vol- 
untary and  involuntary)  are  made  to  contract  as  the  needs 
of  the  body  for  motion  require. 

Energy  Transformation  in  the  Muscle. — The  muscle 
serves  as  a  kind  of  engine,  doing  work  by  the  transforma- 
tion of  potential  into  kinetic  energy.  Evidences  of  this 
are  found  in  the  changes  that  accompany  contraction. 
Careful  study  shows  that  during  any  period  of  contrac- 
tion oxygen  and  food  materials  are  consumed,  waste  prod- 
ucts, such  as  carbon  dioxide,  are  produced,  and  heat  is 


THE   MUSCULAR   SYSTEM 


249 


liberated.  Furthermore,  the  blood  supply  to  the  muscle  is 
such  that  the  materials  for  providing  energy  may  be  car- 
ried rapidly  to  it  and  the  products  of  oxidation  as  rapidly 
removed.  Blood  vessels  penetrate  the  muscles  in  all  di- 
rections and  the  capillaries  lie  very 
near  the  individual  cells  (Fig.  113). 
Provision  is  made  also,  through  the 
nervous  system,  for  increasing  the 
blood  supply  when  the  muscle  is  at 
work.  From  these  facts,  as  well  as 
from  the  great  force  with  which  the 
muscle  contracts,  one  must  conclude 
that  the  muscle  is  a  transformer  of 
energy  —  that  within  its  protoplasm, 
chemical  changes  take  place  whereby 
the  potential  energy  of  oxygen  and 
food  is  converted  into  the  kinetic 
energy  of  motion. 

Plan  of  Using  Muscular  Force.  — 
Two  difficulties  have  to  be  overcome  in  the  using  of 
muscular  force  in  the  body.  The  first  of  these  is  due  to 
the  fact  that  the  muscles  exert  their  force  only  when 
tJiey  contract.  They  can  pull  but  not  push.  Hence,  in 
order  to  bring  about  the  opposing  movements J  of  the 
body,  each  muscle  must  work  against  some  force  that 
produces  a  result  directly  opposite  to  that  which  the 
muscle  produces.  Some  of  the  muscles  (those  of  breath- 
ing) work  against  the  elasticity  of  certain  parts  of  the 
body;  others  (those  that  hold  the  body  in  an  upright 
position),  to  some  extent  against  gravity ; .  and  others 

1  Every  movement  in  the  body  has  its  opposing  movement.  This  is  necessary 
both  on  account  of  the  work  to  be  accomplished  and  for  preserving  the  natural 
form  of  the  body. 


FIG.  113.  —  Capillaries 
of  muscles. 


250  MOTION    AND   COORDINATION 

(the   non-striated    muscle    in  arteries),    against    pressure. 

But  in  most  cases,  muscles  work  against  muscles. 

The  striated,  or  skeletal,  muscles  are  nearly  all  arranged 

after  the  last-named  plan.     As  a  rule  a  pair  of  muscles  is 

so  placed,  with  reference  to  a  joint,  that  one  moves  the 

part  in  one  direction,  and  the 
other  moves  it  in  the  opposite 
direction.  From  the  kinds  of 
motion  which  the  various  muscle 
pairs  produce,  they  are  classified 
as  follows : 

1.  Flexors    and    Extensors. — 
The  flexor  muscles  bend  and  the 

FIG.  114.  —  The  muscle  pair  extensors  straighten  joints  (Fig. 

that  operates  the  forearm.     For     j  j^\ 

names  of  these  muscles,  see  Fig.  .,   ,  ,  ,      ., ,   , 

2.  Adductors    and  Abductors. 
119. 

— The  adductors  draw  the  limbs 

into  positions  parallel  with  the  axis  of  the  body  and  the 
abductors  draw  them  away. 

3.  Rotators   (two    kinds). — The   rotators    are    attached 
about  pivot  joints  and  bring  about  twisting  movements. 

4.  Radiating  and    Sfhincter    Muscles.  —  The  radiating 
muscles  open  and  the  sphincter  muscles  close  the  natural 
openings  of  the  body,  such  as  the  mouth. 

The  pupil  should  locate  examples  of  the  different  kinds  of  muscle 
pairs  in  his  own  body. 

Exchange  of  Muscular  Force  for  Motion.  —  The  second 
difficulty  to  be  overcome  in  the  use  of  muscular  force  in 
the  body  is  due  to  the  fact  that  the  muscles  contract 
through  short  distances,  while  it  is  necessary  for  most  of 
them  to  move  portions  of  the  body  through  long  distances. 
It  may  be  easily  shown  that  the  longest  muscles  of  the 
body  do  not  shorten  more  than  three  or  four  inches  during 


THE   MUSCULAR   SYSTEM  2$  I 

contraction.  To  bring  about  the  required  movements  of 
the  body,  which  in  some  instances  amount  to  four  or  five 
feet,  requires  that  a  large  proportion  of  the  muscular  force 
be  exchanged  for  motion.  The  machines  of  the  skeleton, 
while  providing  for  motion  in  definite  directions,  also  pro- 
vide the  means  whereby  strong  forces,  acting  through  'short 
distances,  are  made  to  produce  movements  of  less  force, 
through  long  distances.  The  mechanical  device  employed 
for  this  purpose  is  known  as 

The  Lever.  —  The  lever  may  be  described  as  a  stiff  bar 
which  turns  about  a  fixed  point  of  support,  called  the  ful- 
crum.     The  force  applied  to  the 
bar  to  make  it  turn  is  called  the  /  /a 

power,  and  that  which  is  lifted          ,4 " 

or  moved  is  termed  the  weight.  ,b 

The  weight,  the  power,  and  the    plj  F  / 

fulcrum    may   occupy   different 
positions  along  the  bar  and  this      ,   ,,  _ 

F__  o  jim 

gives  rise  to  the  three  kinds  of   .A-^'IlT.- — ^,— 

levers,  known  as  levers  of  the 

first  class,  the  second  class,  and  ^                           a 

the  third  class  (Fig.   115).     In      ^ ^— -™"" m 

levers  of  the  first  class  the  f  ul- 

.  .  FIG.  115.  —  Classes  of  levers, 

crum  occupies  a  position  some-  L  Two    leyers    of    first    c]ass 

where  between  the  power  and  showing  fulcrums  in  different 
the  weight.  In  the  second  class  positions.  II.  Lever  of  see- 
the weight  is  between  the  ful-  ond  class-  IIL  Lever  of  third 

class.     F.   Fulcrum.     P.   Power. 

crum   and   the   power.     In  the    w    Weight        a^   Power.arm. 
third  class  the  power  is  between  &  Weight-arm, 
the  fulcrum  and  the  weight. 

Application  to  the  Body.  —  In  the  body  the  bones  serve 
as  levers;  the  turning  points,  or  fulcrums,  are  found  at  the 
joints;  the  muscles  supply  the  power;  and  parts  of  the 


ii 


252  MOTION    AND    COORDINATION 

body,  or  things  to  be  lifted,  serve  as  weights.  For  these 
levers  to  increase  the  motion  of  the  muscles,  it  is  necessary 
that  the  muscles  be  attached  to  the  bones  near  the  joints, 
and  that  the  parts  to  be  moved  be  located  at  some  distance 
from  the  joints.  In  other  words  the  (muscle)  power-arm 
must  be  shorter  than  the  (body)  weight-arm.1 

Examining    Fig.     116,    it    is   seen   that    the    distances 
moved  by  the  power  and  weight  vary  as  their  respective 

distances  from  the  fulcrum. 
/C.  That  is  to  say,  if  the  weight 

/,          •--.._          First  class  lever 

\L  •—-..__   F  is  twice  as  far  from  the  ful- 


—~~ypi    crum  as  the  power,  it  will 
move  through  twice  the  dis- 

Third  class  lever  ° 

tance,  and  if  three  times  as 


UP        "---....  far,  through  three  times  the 

distance.  Thus  the  muscles, 
FIG.      116.  —  Motion      producing   by  acting  through  short  dis- 
levers.      Diagrams  show   relative   dis-    ^^  ,        ^  ^^  arms  Q£ 
tances     moved     by     the     power     and  x 

weight  in  levers    having  the  power  levers),  are    able    to    move 

nearer  the  fulcrum  than  is  the  weight,    portions  of  the  body  (located 
f.  Fulcrum,    p,  P' .  Power.    W,  W.  on  tne  long  arms)  through 

long    distances.      Can    all 
three  classes  of  levers  be  used  in  this  way  in  the  body? 

Classes  of  Levers  found  in  the  Body.  —  Practically  all  of 
the  levers  of  the  body  belong  either  to  the  first  class  or 
the  third  class.  In  both  of  these  the  muscle  power  can 
be  applied  to  the  short  arm  of  the  lever,  thereby  moving 
the  body  weight  through  a  longer  distance  than  the  muscle 
contracts  (Fig.  116).  In  the  levers  of  the  second  class, 
however,  the  weight  occupies  this  position,  being  situated 
between  the  power  and  fulcrum  (Fig.  117).  The  weight, 

1  The  distance  from  the  fulcrum  to  the  power  is  called  the  power-arm  and  the 
distance  from  the  tulcrum  to  the  weight  is  called  the  weight-arm  (Fig.  115). 


THE    MUSCULAR   SYSTEM 


253 


f 


Second  class  lever 


therefore,  cannot  move  far- 
ther than  the  power  in  this 
lever.  It  must  always  move 
a  shorter  distance.  While 

such  a  lever  is  of  great  ad-   f ,/.--' Jjp- 

vantage    in    lifting    heavy     p, 

weights  outside  of  the  body,     \ 

it  cannot  be  used  f  or  increas-    JIG'  "7- -Weight  lifting  levers. 

-     ,  Diagrams      show      relative      distances 

mg  the  motion  of  the  mus-    moved  by  the  power  and  weight  in 

cles.    For  this  reason  no  well-     levers    having    the  weight  nearer    the 

defined  levers  of  the  second    fulcrum  than  is  the  power.    F.  Ful- 
classarepresentinthebody.1    crum'  P'  p'  Power'  w>  w'-  Weieht- 
Loss  of  Muscular  Force.  —  Using  a  small  spring  balance 
for  measuring  the  power,  a  light  stick  for  a  lever,  and 
a  small  piece  of  metal  for  a  weight, 
and    arranging    these   to    represent 
some    lever "  of   the    body    (as    the 

1  The  foot  in  lifting  the  body  on  tiptoe  appears 
at  first  thought  to  be  a  lever  of  the  second  class, 
the  body  being  the  weight  and  the  toe  serving  as 
the  'fulcrum.  However,  if  the  distance  which  the 
body  is  raised  is  compared  with  the  distance  which 
the  muscle  shortens,  it  is  found  that  the  supposed 
weight  has  moved  farther  than  the  power  (Fig. 
118).  It  will  also  be  noted  that  the  muscle  which 
furnishes  the  power  is  attached  at  its  upper  end  to 
the  "weight."  These  facts  show  clearly  that  we 
are  not  here  dealing  with  a  lever  of  the  second 
FIG.  1 1 8. — Diagram  of  c]ass  The  foot  in  this  instance  acts  as  a  lever  of 
the  foot  lever.  F.  Fulcrum  the  first  class  with  the  fulcrum  at  the  ankle  joint 
at  ankle  joint.  W.  Body  and  the  toe  pressing  against  the  earth,  which  is  the 
weight  expressed  as  pres-  actual  weight.  Since  the  earth  is  immovable,  the 
sure  against  the  earth,  body  is  lifted  or  pushed  upward,  somewhat  as  a 
While  the  muscle  power  fulcrum  support  is  made  to  move  when  it  is  too 


Knee  joint 


acts  through  the  distance  ab, 


weak  to  hold  up  the  weight  that  is  being  lifted. 


In  other  words,  we  have  the  same  lever  action  in 
the  fulcrum  support  (body) 

rr  v  *  '  the  foot  in  lifting  the  body  as  we  have  when  one 
is  forced  through  the  dis-  ]ies  face  downward>  and>  bending  the  knee,  lifts 
tance  rh.  some  object  on  the  toes. 


254  MOTION    AND    COORDINATION 

forearm),  it  is  easily  shown  that  the  gain  in  motion 
causes  a  corresponding  loss  in  muscular  power.  (See 
Practical  Work.)  If,  for  example,  the  balance  is  attached 
two  inches  from  the  fulcrum  and  the  weight  twelve  inches, 
the  pull  on  the  balance  is  found  to  be  six  times  greater 
than  the  weight  that  is  being  lifted.  If  other  positions  are 
tried,  it  is  found  that  the  power  exerted  in  each  case  is  as 
many  times  greater  than  the  weight  as  the  weight-arm  is 
times  longer  than  the  power-arm. 

Applying  this  principle  to  the  levers  of  the  body,  it 
is  seen  that  the  gain  in  motion  is  at  the  expense  of 
muscular  force,  or,  as  we  say,  muscular  force  is  exchanged 
for  motion.  This  exchange  is  greatly  to  the  advantage 
of  the  body ;  for  while  the  ability  to  lift  heavy  weights 
is  important,  the  ability  to  move  portions  of  the  body 
rapidly  and  through  long  distances  is  much  more  to  be 
desired. 

Important  Muscles.  —  There  are  about  five  hundred  sep- 
arate muscles  in  the  body.  These  vary  in  size,  shape,  and 
plan  of  attachment,  to  suit  their  special  work.  Some  of 
those  that'  are  prominent  enough  to  be  felt  at  the  surface 
are  as  follows  : 

Of  the  head :  The  temporal,  in  the  temple,  and  the  mas- 
seter,  in  the  cheek.  These  muscles  are  attached  to  the 
lower  jaw  and  are  the  chief  muscles  of  mastication. 

Of  the  neck:  The  sterno-mastoids,  which  pass  between 
the  mastoid  processes,  back  of  the  ears,  and  the  upper 
end  of  the  sternum.  They  assist  in  turning  the  head  and 
may  be  felt  at  the  sides  of  the  neck  (Fig.  119). 

Of  the  upper  arm:  The  biceps  on  the  front  side,  the 
triceps  behind,  and  the  deltoid  at  the  upper  part  of  the 
arm  beyond  the  projection  of  the  shoulder. 

Of  the  forearm :  The  flexors  of  the  fingers,  on  the  front 


THE   MUSCULAR   SYSTEM 


255 


Triceps-- 


Latissimus  Dorsi 


Sluteus  Maximus- 


Vastus  Extern  us 


xtensors  of  Fingers 
Flexors  of  Fingers 


—  Rectus  Abdominis 


FIG.  119.  —  Back  and  front  views  of  important  muscles. 


2$6  MOTION   AND   COORDINATION 

side,  and  the  extensors  of  the  fingers,  on  the  back  of  the 
forearm  (Fig.  119). 

Of  the  hand:  The  adductor  pollicis  between  the  thumb 
and  the  palm. 

Of%  the  trunk :  The  pectoralis  major,  between  the  upper 
front  part  of  the  thorax  and  the  shoulder ;  the  trapezius, 
between  the  back  of  the  shoulders  and  the  spine ;  the  recttis 
abdominiSj  passing  over  the  abdomen  from  above  down- 
ward ;  and  \hzerector  spina,  found  in  the  small  of  the  back. 

Of  the  hips:  The  glutens  maximus,  fastened  between  the 
lower  back  part  of  the  hips  and  the  upper  part  of  the  femur. 

Of  the  upper  part  of  the  leg:  The  rectus  femoris,  the  large 
muscle  on  the  front  of  the  leg  which  connects  at  the  lower 
end  with  the  kneepan. 

Of  the  lower  leg:  The  tibia  Us  anticus  on  the  front  side, 
exterior  to  the  tibia,  and  the  gastrocnemins,  the  large  mus- 
cle in  the  calf  of  the  leg.  This  is  the  largest  muscle  of  the 
body,  and  is  connected  with  the  heel  bone  by  the  tendon 
of  Achilles  (Fig.  1 19). 

The  use  of  these  muscles  is,  in  most  instances,  easily 
determined  by  observing  the  results  of  their  contraction. 

HYGIENE   OF  THE   MUSCLES 

The  hygiene  of  the  muscles  is  almost  expressed  by  the 
one  word  exercise.  It  is  a  matter  of  everyday  knowledge 
that  the  muscles  are  developed  and  strengthened  by  use, 
and  that  they  become  weak,  soft,  and  flabby  by  disuse. 
The  effects  of  exercise  are,  however,  not  limited  to  the 
large  muscles  attached  to  the  skeleton,  but  are  apparent 
also  upon  the  involuntary  muscles,  whose  work  is  so  closely 
related  to  the  vital  processes.  While  it  is  true  that  exer- 
cise cannot  be  applied  directly  to  the  involuntary  muscles, 
it  is  also  true  that  exercise  of  the  voluntary  muscles  causes 


THE   MUSCULAR   SYSTEM  257 

a  greater  activity  on  the  part  of  those  that  are  involuntary 
and  is  indirectly  a  means  of  exercising  them. 

Exercise  and  Health.  —  In  addition  to  its  effects  upon 
the  muscles  themselves,  exercise  is  recognized  as  one  of 
the  most  fundamental  factors  in  the  preservation  of  the 
health.  Practically  every  process  of  the  body  is  stimulated 
and  the  body  as  a  whole  invigorated  by  exercise  properly 
taken.  On  the  other  hand,  a  lack  of  exercise  has  an  effect 
upon  the  entire  body  somewhat  similar  to  that  observed 
upon  a  single  muscle.  It  becomes  weak,  lacks  energy,  and 
in  many  instances  actually  loses  weight  when  exercise  is 
omitted.  This  shows  exercise  to  supply  an  actual  need 
and  to  be  in  harmony  with  the  nature  and  plan  of  the 
body. 

How  Exercise  benefits  the  Body.  —  In  accounting  for  the 
healthful  effects  of  exercise,  it  must  be  borne  in  mind 
that  the  body  is  essentially  a  motion-producing  structure. 
Furthermore,  its  plan  is  such  that  the  movements  of  its 
different  parts  aid  indirectly  the  vital  processes.  The 
student  will  recall  instances  of  such  aid,  as,  for  example, 
the  assistance  rendered  by  muscular  contractions  in  the 
circulation  of  the  blood  and  lymph,  due  to  the  valves  in 
veins  and  lymph  vessels,  and  the  assistance  rendered  by  ab- 
dominal movements  in  the  propulsion  of  materials  through 
the  food  canal.  A  fact  not  as  yet  brought  out,  however, 
is  that  exercise  stimulates  nutritive  changes  in  the  cells, 
thereby  imparting  to  them  new  vigor  and  vitality.  While 
this  effect  of  exercise  cannot  be  fully  accounted  for,  two 
conditions  that  undoubtedly  influence  it  are  the  following? 

1.  Exercise  causes  the  blood  to  circulate  more  rapidly. 

2.  Exercise    increases    the    movement   of    the    lymph 
through  the  lymph  vessels. 

The  increase  in  the  flow  of  the  blood  and  the  lymph 


258  MOTION    AND   COORDINATION 

causes  changes  to  take  place  more  rapidly  in  the  liquids 
around  the  cells,  thereby  increasing  the  supply  of  food 
and  oxygen,  and  hastening  the  removal  of  waste. 

One  should  plan  for  Exercise.  —  Since  exercise  is  de- 
manded by  the  nature  and  plan  of  the  body,  to  neglect  it 
is  a  serious  matter.  People  do  not  purposely  omit  exer- 
cise, but  from  lack  of  time  or  from  its  interference  with  the 
daily  routine  of  duties,  the  needed  amount  is  frequently 
not  taken.  Especially  is  this  true  of  students  and  others 
who  follow  sedentary  occupations.  People  of  this  class 
should  plan  for  exercise  as  they  plan  for  the  other  great 
needs  of  the  body  —  food,  sleep,  clothing,  etc.  It  is  only 
by  making  a  sufficient  amount  of  muscular  work  or  play  a 
regular  part  of  the  daily  program  that  the  needs  of  the 
body  for  exercise  are  adequately  supplied. 

Amount  and  Kind  of  Exercise.  —  The  amount  of  exer- 
cise required  varies  greatly  with  different  individuals,  and 
definite  recommendations  cannot  be  made.  For  each  indi- 
vidual also  the  amount  should  vary  with  the  physical  con- 
dition and  the  other  demands  made  upon  the  energy. 
One  in  health  should  exercise  sufficiently  to  keep  the  mus- 
cles firm  to  the  touch  and  the  body  in  a  vigorous  condition. 

Of  the  many  forms  of  exercise  from  which  one  may 
choose,  the  question  is  again  one  of  individual  adaptability 
and  convenience.  While  the  different  forms  of  exercise 
vary  in  their  effects  and  may  be  made  to  serve  different 
purposes,  the  consideration  of  these  is  beyond  the  scope  of 
an  elementary  text.  As  a  rule  one  will  not  go  far  wrong 
by  following  his  inclinations,  observing  of  course  the  con- 
ditions under  which  exercise  is  taken  to  the  best  advantage. 

General  Rules  for  Healthful  Exercise. — That  exercise 
may  secure  the  best  results  from  the  standpoint  of  health, 
a  number  of  conditions  should  be  observed:  i.  It  should 


THE   MUSCULAR   SYSTEM  259 

not  be  excessive  or  carried  to  the  point  of  exhaustion. 
Severe  physical  exercise  is  destructive  to  both  muscular 
and  nervous  tissues.  2.  It  should,  if  possible,  be  of  an 
interesting  nature  and  taken  in  the  open  air.  3.  It  should 
be  counter-active,  that  is,  calling  into  play  those  parts  of 
the  body  that  have  not  been  used  during  the  regular  work.1 
4.  It  should  be  directed  toward  the  weak  rather  than 
toward  the  strong  parts  of  .the  body.  5.  When  one  is 
already  tired  from  study,  or  other  work,  it  should  be  taken 
with  moderation  or  omitted  for  the  time  being.  (For  exer- 
cise of  the  heart  muscle  and  the  muscular  coat  of  the  blood 
vessels  see  pages  55  and  57.) 

Massage.  —  In  lieu  of  exercise  taken  in  the  usual  way, 
similar  effects  are  sometimes  obtained  by  a  systematic  rub- 
bing, pressing,  stroking,  or  kneading  of  the  skin  and  the 
muscles  by  one  trained  in  the  art.  This  process,  known 
as  massage,  may  be  gentle  or  vigorous  and  is  subject  to  a 
variety  of  modifications.  Massage  is  applied  when  one  is 
unable  to  take  exercise,  on  account  of  disease  or  accident, 
and  also  in  the  treatment  of  certain  bodily  disorders.  A 
weak  ankle,  wrist,  or  other  part  of  the  body,  or  even  a 
bruise,  may  be  greatly  benefited  by  massage.  The  flow 
of  blood  and  lymph  is  stimulated,  causing  new  materials 
to  be  passed  to  the  affected  parts  and  waste  materials  to 
be  removed.  Massage,  however,  should  never  be  applied 
to  a  boil,  or  other  infected  sore.  The  effect  in  this  case 
would  be  to  spread  the  infection  and  increase  the  trouble. 

Summary.  —  Motion  is  provided  for  in  the  body  mainly 
through  the  muscle  cells.  These  are  grouped  into  working 
parts,  called  muscles,  which  in  turn  are  attached  to  the 
movable  parts  of  the  body.  The  striated  muscles,  as  a 

i  Walking  is  considered  one  of  the  very  best  forms  of  counter-active  exercise 
for  the  brain  worker  (page  328). 


260  MOTION    AND   COORDINATION 

rule,  are  attached  to  the  mechanical  devices  found  in  the 
skeleton,  and  bring  about  the  voluntary  movements.  The 
non-striated  muscles  surround  the  parts  on  which  they 
act,  and  produce  involuntary  movements.  Both,  however, 
are  under  the  control  of  the  nervous  system.  To  bring 
about  the  opposing  movements  of  the  body,  the  striated 
muscles  are  arranged  in  pairs  ;  and  to  increase  their  motion, 
the  bones  are  used  as  levers.  Physical  exercise  is  neces- 
sary both  for  the  development  of  the  muscles  and  for  the 
health  and  vigor  of  the  entire  body. 

Exercises.  —  i.  Compare  the  striated  and  non-striated  muscles  with 
reference  to  structure,  location,  and  method  of  work. 

2.  In  what  respects  is  the  muscular  tissue  of  the  heart  like  the  striated, 
and  in  what  respects  Jike  the  non-striated,  muscular  tissue  ? 

3.  If  muscles  could  push  as  well  as  pull,  would  so  many  be  needed 
in  the  body  ?     Why  ? 

4.  Locate  muscles  that  work  to  some  extent  against  elasticity  and 
gravity. 

5.  Locate  five  muscles  that  act  as  flexors ;    five  that  act  as  exten- 
sors ;    two   that  act   as   adductors ;    and   two   as   abductors.      Locate 
sphincter  and  radiating  muscles. 

6.  By  what  means  does  the  nervous  system  control  the  muscles  ? 

7.  Give  proofs  of  the  change  of  potential  into  kinetic  energy  during 
muscular  contraction. 

8.  Define  the  essential  properties  of  muscular  tissue  and  state  the 
purpose  served  by  each. 

9.  Describe  a  lever.     For  what  general  purpose  are  levers  used  in 
the  body  ?     What  other  purpose  do  they  serve  outside  of  the  body  ? 

10.  Why  are  levers  of  the  second  class  not  adapted  to  the  work  of 
the  body  ? 

u.  Name  the  class  of  lever  used  in  bending  the  elbow  ;  in  straight- 
ening the  elbow ;  in  raising  the  knee ;  in  elevating  the  toes ;  and  in 
biting.  Why  is  one  able  to  bite  harder  with  the  back  teeth  than  with 
the  front  ones  when  the  same  muscles  are  used  in  both  cases? 

12.  Measure  the  distance  from  the  middle  of  the  palm  of  the  hand 
to  the  center  of  the  elbow  joint.  Find  the  attachment  of  the  tendon 
of  the  biceps  muscle  to  the  radius  and  measure  its  distance  to  the 


THE   MUSCULAR   SYSTEM  26 1 

center  of  the  elbow  joint.  From  these  distances  calculate  the  force 
with  which  the  biceps  contracts  in  order  to  support  a  weight  of  ten 
pounds  on  the  palm  of  the  hand. 

13.  How  does  exercise   benefit   the   health  ?     How   does   a  short 
walk  "  clear  the  brain  "  and  enable  one  to  study  to  better  advantage  ? 

14.  When  exercise  is   taken  for  its  effects  upon   the  health,  what 
conditions  should  be  observed? 

PRACTICAL  WORK 

The  reddish  muscle  found  in  a  piece  of  beef  is  a  good  example  of 
striated  muscle.  The  clear  ring  surrounding  the  intestine  of  a  cat 
(shown  by  cross  section)  and  the  outer  portion  of  the  preparation  from 
the  cow's  stomach,  sold  at  the  butcher  shop  under  the  name  of  tripe, 
are  good  examples  of  non-striated  muscular  tissue.  The  heart  of  any 
animal,  of  course,  shows  the  heart  muscle. 

To  show  the  Structure  of  Striated  Muscle.  —  Boil  a  tough  piece  of 
beef,  as  a  cut  from  the  neck,  until  the  connective  tissue  has  thoroughly 
softened.  Then  with  some  pointed  instrument,  separate  the  main  piece 
into  its  fiber  bundles  and  these  in  turn  into  their  smallest  divisions. 
The  smallest  divisions  obtainable  are  the 'muscle  cells  or  fibers. 

To  show  Striated  Fibers. — r  Place  a  small  muscle  from  the  leg  of  a 
frog  in  a  fifty-per-cent  solution  of  alcohol  and  leave  it  there  for  half  a  day 
or  longer.  Then  cover  with  water  on  a  glass  slide,  and  with  a  couple 
of  fine  needles  tease  out  the  small  muscle  threads.  Protect  with  a 
cover  glass  and  examine  with  a  microscope,  first  with  a  low  and  then 
with  a  high  power.  The  striations,  sarcolemma,  and  sometimes  the 
nuclei  and  nerve  plates,  may  be  distinguished  in  such  a  preparation. 

To  show  Non-striated  Cells.  —  Place  a  clean  section  of  the  small 
intestine  of  a  cat  in  a  mixture  of  one  part  of  nitric  acid  and  four  parts 
of  water  and  leave  for  four  or  five  hours.  Thoroughly  wash  out  the  acid 
with  water  and  separate  the  muscular  layer  from  the  mucous  membrane. 
Cover  a  small  portion  of  the  muscle  with  water  on  a  glass  slide  and 
tease  out,  with  needles,  until  it  is  as  finely  divided  as  possible.  Ex- 
amine with  a  microscope,  first  with  a  low  and  then  with  a  high  power. 
The  cells  appear  as  very  fine,  spindle-shaped  bodies. 

To  illustrate  Muscular  Stimulus  and  Contraction.  —  Separate  the 
muscles  at  the  back  of  the  thigh  of  a  frog  which  has  just  been  killed 
and  draw  the  large  sciatic  nerve  to  the  surface.  Cut  this  as  high  up  as 
possible  and,  with  a  sharp  knife  and  a  small  pair  of  scissors,  dissect  it 


262 


MOTION    AND   COORDINATION 


out  to  the  knee.  Now  cut 'out  entirely  the  large  muscle  of  the  calf  of 
the  leg  (the  gastrocnemius),  but  leave  attached  to  it  the  nerve,  the 
lower  tendon,  and  the  bones  of  the  knee. 
Mount  on  an  upright  support,  as  shown  in 
Fig.  1 20,  and  fasten  the  tendon  to  a  lever 
below  by  a  thread  or  small  wire  hook : 

i.  Lay  the  nerve  over  the  ends  of  the 
wires  from  a  small  battery  which  are  attached 
to  the  support  at  A,  and  arrange  a  second 

FIG.  120. Apparatus    break  in  the  circuit  at  S.  .At  this  place  the 

for  demonstrating  proper-    battery  circuit  is  made  and  broken  either  by 

ties  of  muscles.  a  telegraph  key  or  by  simply  touching  and 

separating  the  wires.     Note  that  the  muscle 

gives  a  single  contraction,  or  twitch,  both  when  the  current  is  made 
and  when  it  is  broken. 

2.  Remove  the  current  and  pinch  the  end  of  the  nerve,  noting  the 
result.     With  very  fine  wires,  connect  the  battery  directly  to  the  ends 
of  the  muscle.     Stimulate   by  making  and   breaking  the   current   as 
before.      In   this  experiment   the  muscle  cells  are  stimulated   by  the 
direct  action  of  the  current  and  not  by  the  current  acting  on  the  nerve. 

3.  With  the  wires  attached  to  either  the  muscle  or  the  nerve,  make 
and  break  the  current  in  rapid  succession.     This  causes  the  muscle  to 
enter  into  a  second  contraction  before  it  has  relaxed  from  the  first,  and 
if  the  shocks  follow  in  rapid  succession,  to  continue  in  the  contracted 
state.     This  condition,  which  represents  the  method  of  contraction  of 
the  muscles  in  the  body,  is  called  tetanus. 

NOTE.  —  In  these  experiments  a  twitching  of  the  muscle  is  frequently 
observed  when  no  stimulus  is  being  applied.  This  is  due  to  the  drying 
out  of  the  nerve  and  is  prevented  by  keeping  it  wet  with  a  physiological 
salt  solution.  (See  footnote,  page  38.) 

To  show  the  Action  of  Levers.  —  With  a  light  but  stiff  wooden 
bar,  a  spring  balance,  and  a  wedge-shaped  fulcrum,  show: 

1 .  The  position  of  the  weight,  the  fulcrum,  and  the  power  in  the 
different  classes  of  levers,  and  also  the  weight-arm  and  the  power-arm 
in  each  case. 

2.  The  direction  moved  by  the  power  and  the  weight  respectively 
in  the  use  of  the  different  classes  of  levers. 

3.  That  when  the  power-arm  and  weight-arm  are  equal,  the  power 
equals  the  weight  and  moves  through  the  same  distance. 


THE   MUSCULAR   SYSTEM  263 

4.  That  when  the  power-arm  is  longer  than  the    weight-arm,   the 
weight  is  greater,  but  moves  through  a  shorter  distance  than  the  power. 

5.  That  when  the  weight-arm   is   longer  than  the  power-arm,  the 
power  is  greater  and  moves  through  a  shorter  distance  than  the  weight. 

To  show  the  Loss  of  Power  in  the  Use  of  the  Body  Levers.  — 
Construct  a  frame  similar  to,  but  larger  than,  that  shown  in  Fig.  120, 
(about  12  inches  high),  and  hang  a  small  spring  balance  (250  grams 
capacity)  at  the  place  where  the  muscle  is  attached.  Fasten  the  end 
of  a  lever  to  the  upright  piece,  at  a  point  on  a  level  with  the  end  of  the 
balance  hook.  (The  nail  or  screw  used  for  this  purpose  must  pass 
loosely  through  the  lever,  and  serve  as  a  pivot  upon  which  it  can  turn.) 
The  lever  should  consist  of  a  light  piece  of  wood,  and  should  have  a 
length  at  least  three  times  as  great  as  the  distance  from  the  hook  to 
the  turning  point.  Connect  the  balance  hook  with  the  lever  by  a 
thread  or  string,  and  then  hang  upon  it  a  small  body  of  known  weight. 
Note  the  amount  of  force  exerted  at  the  balance  in  order  to  support  the 
weight  at  different  places  on  the  lever.  At  what  point  is  the  force  just 
equal  to  the  weight?  Where  is  it  twice  as  great?  Where  three  times? 
Show  that  the  force  required  to  support  the  weight  increases  propor- 
tionally as  the  weight-arm  and  as  the  distance  through  which  the 
weight  may  be  moved  by  the  lever.  Apply  to  the  action  of  the  biceps 
muscle  in  lifting  weights  on  the  forearm. 

A  Study  of  the  Action  of  the  Biceps  Muscle.  —  Place  the  fingers 
upon  the  tendon  of  the  biceps  where  it  connects  with  the  radius  of  the 
forearm.  With  the  forearm  resting  upon  the  table,  note  that  the  ten- 
don is  somewhat  loose  and  flaccid,  but  that  with  the  slightest  effort 
to  raise  the  forearm  it  quickly  tightens.  Now  transfer  the  fingers  to 
the  body  of  the  muscle,  and  sweep  the  forearm  through  two  or  three 
complete  movements,  noting  the  changes  in  the  length  and  thickness 
of  the  muscle.  Lay  the  forearm  again  on  the  table,  back  of  hand  down, 
and  place  a  heavy  weight  (a  flatiron  or  a  hammer)  upon  the  hand. 
Note  the  effort  required  to  raise  the  weight,  and  then  shift  it  along  the 
arm.  Observe  that  the  nearer  it  approaches  the  elbow  the  lighter  it 
seems.  Account  for  the  difference  in  the  effort  required  to  raise  the 
weight  at  different  places.  Does  the  effort  vary  as  the  distance  from 
the  tendon? 


CHAPTER   XVI 
THE  SKIN 

PROTECTIVE  coverings  are  found  at  all  the  exposed  sur- 
faces of  the  body.  These  vary  considerably  at  different 
places,  each  being  adapted  to  the  conditions  under  which 
it  serves.  The  most  important  ones  are  the  skin,  which 
covers  the  entire  external  surface  of  the  body;  the  mucous 
membrane,  which  lines  all  the  cavities  that  communicate 
by  openings  with  the  external  surface;  and  the  serous 
membrane,  which,  including  the  synovial  membranes,  lines 
all  the  closed  cavities  of  the  body.  In  addition  to  the 
protection  which  it  affords,  the  skin  is  one  of  the  means 
by  which  the  body  is  brought  into  proper  relations  with 
its  surroundings.  It  is  because  of  this  function  that  we 
take  up  the  study  of  the  skin  at  this  time. 

The  Skin  is  one  of  the  most  complex  structures  of  the 
body,  and  serves  several  distinct  purposes.  It  is  estimated 
to  have  an  area  of  from  14  to  16  square  feet,  and  to  have 
a  thickness  which  varies  from  less  than  one  eighth  to 
more  than  one  fourth  of  an  inch.  It  is  thickest  on  the 
palms  of  the  hands  and  the  soles  of  the  feet,  the  places 
where  it  is  most  subject  to  wear.  It  is  made  up  of  two 
distinct  layers  —  an  outer  layer  called  the  epidermis,  or 
cuticle,  and  an  inner  layer  called  the  dermis,  or  cutis  vera 
(Fig.  12 1). 

The  Dermis.  —  This  is  the  thicker  and  heavier  of  the 
two  layers,  and  is  made  up  chiefly  of  connective  tissue. 
The  network  of  tough  fibers  which  this  tissue  supplies, 

264 


THE    SKIN 


265 


forms  the  essential  body  of  the  dermis  and  gives  to  it  its 
power  of  resistance.  It  is  on  account  of  the  connective 
tissue  that  the  skins  of  animals  can  be  converted  into 
leather  by  tanning.  A  variety  of  structures,  including 


FIG.  121.  —  Section  of  skin  magnified,  a,  b.  Epidermis,  b.  Pigment  layer. 
c.  Papilla,  d.  Dermis.  e.  Fatty  tissue.  /,  g,  h.  Sweat  gland  and  duct. 
i,  k.  Hair  and  follicle.  /.  Oil  gland. 

blood  and  lymph  vessels,  oil  and  perspiratory  glands,  hair 
follicles,  and  nerves,  are  found  embedded  in  the  connective 
tissue  (Fig.  122).  These  aid  in  different  ways  in  the  work 
of  the  skin. 

On  the  outer  surface  of  the  dermis  are  numerous  eleva- 


266 


COORDINATION    AND    SENSATION 


tions,  called  papilla.      These  average  about  one  one-hun- 
dredth of  an  inch  in  height,  and  one  two  hundred  and 

fiftieth  of  an  inch  in 
diameter. 

\  \Epidermia      most 
[J 
.Muscte 


Arte, 


.Connective 
tissue 


Dermi's 


Con 


Fat 


FIG.  122.  —  Diagram  of  section  of  skin  showing 
its  different  structures. 


They  are 
numerous  on 
the  palms  of  the 
hands,  the  soles  of 
the  feet,  and  the 
under  surfaces  of  the 
fingers  and  toes.  At 
these  places  they  are 
larger  than  in  other 
parts  of  the  body, 
and  are  closely 
grouped,  forming 
the  parallel  curved  ridges  which  cover  the  surfaces. 
Each  papilla  contains  a  loop  of  capillaries  and  a  small 
nerve,  and  many  of  them  are  crowned  with  touch 
corpuscles  (page  342). 

The  Epidermis  is  much  thinner  than  the  dermis.  It  is 
made  up  of  several  layers  of  cells  which  are  flat  and  scale- 
like  at  the  surface,  but  are  rounded  in  form  where  the 
epidermis  joins  the  dermis.  The  epidermis  has  the  ap- 
pearance of  being  moulded  onto  the  dermis,  filling  up  the 
depressions  between  the  papillae  and  having  correspond- 
ing irregularities  (Fig.  121).  No  blood  vessels  are  found 
in  the  epidermis,  its  nourishment  being  derived  from  the 
lymph  which  reaches  it  from  the  dermis. .  Only  the  part 
next  to  the  dermis  is  made  up  of  living  cells.  These  are 
active,  however,  in  the  formation  of  new  cells,  which  take 
the  place  of  those  that  are  worn  off  at  the  surface.  Some 
of  the  cells  belonging  to  the  inner  layer  of  epidermis  con- 
tain pigment  granules,  which  give  the  skin  its  color  (Fig. 


THE    SKIN  267 

12 1).  The  epidermis  contains  no  nerves  and  is  therefore 
non-sensitive.  The  hair  and  the  nails  are  important 
modifications  of  the  epidermis. 

A  Hair  is  a  slender  cylinder,  formed  by  the  union  of 
epidermal  cells,  which  grows  from  a  kind  of  pit  in  the 
dermis,  called  the  hair  follicle.  The  oval  and  somewhat 
enlarged  part  of  the  hair  within  the  follicle  is  called  the 
root,  or  bulb,  and  the  uniform  cylinder  beyond  the  follicle 
is  called  the  shaft.  Connected  with  the  sides  of  the  follicles 
are  the  oil,  or  sebaceous,  glands  (Figs.  121  and  122). 
These  secrete  an  oily  liquid  which  keeps  the  hair  and 
cuticle  soft  and  pliable.  Attached  to  the  inner  ends  of  the 
follicles  are  small,  involuntary  muscles  whose  contractions 
cause  the  roughened  condition  of  the  skin  that  occurs  on 
exposure  to  cold. 

A  Nail  is  a  tough  and  rather  horny  plate  of  epidermal 
tissue  which  grows  from  a  depression  in  the  dermis,  called 
the  matrix.  The  back  part  of  the  nail 
is  known  as  the  root,  the  middle  convex 
portion  as  the  body,  and  the  front  margin 
a.s  the.  free  edge  (¥\g.  123).  Material  for 
the  growth  of  the  nail  is  derived  from 

the  matrix,  which  is   lined  with  active      FIG.  123.  — Section 
,    .       ...  ..    ,    of  end  of  finger  show- 

epidermal   cells  and  is  richly  supplied  ing  nail  in  position. 

with  blood  vessels.     Cells  added  to  the 
root  cause  the  nail  to  grow  in  length  (forward)  and  cells 
added  to  the  under  surface  cause  it  to  grow  in  thickness. 
The  cuticle  adheres  to  the  nail  around  its  entire  circum- 
ference so  that  the  covering  over  the  dermis  is  complete. 

Functions  of  the  Skin.  —  The  chief  function  of  the  skin 
is  that  of  protection.  It  is  able  to  protect  the  body  on 
account  of  the  tough  connective  tissue  in  the  dermis,  the 
non-sensitive  cells  of  the  epidermis,  and  also  by  the  touch 


268  COORDINATION   AND    SENSATION 

corpuscles  and  their  connecting  nerve   fibers.     This  pro- 
tection is  of  at  least  three  kinds,  as  follows : 

1.  From  mechanical  injuries  such  as  might  result  from 
contact  with   hard,  rough,  or  sharp  objects.     The  main 
quality  needed  for  resisting  mechanical  injuries  is  tough- 
ness, and  this  is  supplied  both  by  the  epidermis  and  by  the 
connective  tissue  of  the  dermis. 

2.  From  chemical  injuries  caused  by  contact"  with  various 
chemical  agents,  as  acids,  alkalies,  and  the  oxygen  of  the 
air.     The  epidermis,  being  of  such  a  nature  as  to  resist  to 
a  considerable  extent  the  action  of  chemical  agents,  affords 
protection  from  these  substances.1 

3.  From  disease  germs  which  are  everywhere  present. 
The  epidermis  is  the  main  protective  agent  against  attacks 
of  germs,  but  should  the  epidermis  be  broken,  they  meet 
with  further  resistance  from  the  fluids  of  the  dermis  and 
the  white  corpuscles  of  the  blood. 

4.  From   an   excessive   evaporation   of   liquid  from    the 
surface  of  the  body.      In  the  performance   of   this  func- 
tion,  the   skin    is    an   important   means   of    keeping   the 
tissues  soft  and  the  blood  and  lymph  from  becoming  too 
concentrated. 

Other  Functions  of  the  Skin.  —  Through  the  perspiratory 
glands  the  skin  is  an  organ  of  excretion.  While  the  secre- 
tion from  a  single  gland  is  small,  the  waste  that  leaves  the 
body  through  all  of  the  perspiratory  glands  is  considerable2 
(page  206).  By  means  of  the  nerves  terminating  in  the 
touch  corpuscles,  the  skin  serves  as  the  organ  of  touch,  or 
feeling  (Chapter  XX).  To  a  slight  extent  also  the  skin 

1  The  epidermis  does  not  afford  complete  protection  against  chemicals,  many 
of  them  being  able  to  destroy  it  quickly.    The  rule  of  washing  the  skin  immediately 
after  contact  with  strong  chemical  agents  should  always  be  followed. 

2  "  Rough  calculations  have  placed  the  number  of  sweat  glands  on  the  entire 
body  at  about  2,000,000."     Rettger,  Studies  in  Advanced  Physiology. 


THE   SKIN  269 

may  absorb  liquid  substances,  these  being  taken  up  by  the 
blood  and  lymph  vessels,  and  perform  a  respiratory  func- 
tion, throwing  off  carbon  dioxide.  But  the  most  important 
function  of  the  skin,  in  addition  to  protection,  is  that  of 
serving  as 

An  Organ  of  Adaptation.  —  Forming,  as  it  does,  the 
boundary  between  the  body  and  its  physical  environment, 
the  skin  is  perhaps  the  most  important  agent  through 
which  the  body  is  adapted  to  its  immediate  surroundings. 
Evidence  of  this  is  found  in  the  great  variety  of  influences 
which  are  able  to  affect  the  body  through  their  action 
upon  the  nerves  in  the  skin,  and  in  the  changes  which  the 
epidermis  undergoes  on  exposure.  The  latter  function 
is  especially  marked  in  the  lower  animals,  the  coverings 
of  epidermal  tissue  (hair,  scales,  feathers,  etc.)  adapting 
each  species  to  the  physical  conditions  under  which 
it  lives.  In  man  the  most  striking  example  of  adapta- 
tion through  the  skin  is  seen  in  the  variations  in  the 
quantity  of  blood  circulating  through  it,  corresponding 
to  the  changes  in  the  temperature  outside  of  the  body. 
These  variations  are  of  great  importance,  having  to  do 
with  the 

Maintenance  of  the  Normal  Temperature.  —  It  is  neces- 
sary to  the  continuance  of  life  that  the  temperature  of  the 
body  be  kept  at  a  nearly  uniform  degree,  called  the  normal 
temperature,  which  is  about  98.6°  F.  The  maintenance  of 
the  normal  temperature  depends  mainly  upon  four  condi- 
tions :  the  chemical  changes  at  the  cells,  the  circulation  of 
the  blood,  the  nervous  system,  and  the  skin.  The  chemical 
changes  produce  the  heat,  the  blood  in  its  circulation  dis- 
tributes the  heat  over  the  body,  and  the  nervous  system  con- 
trols the  heat-producing  and  distributing  processes  (page 
320).  The  skin  is  the  chief  means  by  which  the  body 


2/0  COORDINATION    AND    SENSATION 

gets   rid  of  an   excess   of   heat   and,  by   so   doing,  avoids 
overheating.1 

How  the  Skin  cools  the  Body. —The  skin  is  a  means 
of  ridding  the  body  of  an  excess  of  heat  in  at  least  two 
ways  : 

1.  By  the  conduction  and  radiation  of  heat  from  its  sur- 
face as  from  a  stove.     This  goes  on  all  the  time,  but  varies 
with  the  amount  of  heat  brought  to  the  surface   by  the 
blood. 

2.  By  the  evaporation  of  the  perspiration.     It  is  a  well- 
established  and  easily  demonstrated  principle  that  liquids 
in  evaporating  use  up  heat.     (See  Practical  Work.)     It  is 
also  a  matter  of  everyday  experience  that  the  perspiration 
has  a  cooling  effect  upon  the  body  and  that  its  flow  in- 
creases with  the  amount  of  heat  to  be  gotten  rid  of.     The 
quantity  of   perspiration    secreted,  and  of    heat  disposed 
of  through  its  evaporation,  also  varies  with  the  amount  of 
blood  circulating  through  the  skin. 

Temperature  Regulation  by  the  Skin. — Variations  in 
the  quantity  of  blood  circulating  through  the  skin  enable 
this  organ  to  throw  off  just  the  right  amount  of  heat  for 
keeping  the  body  at  the  normal  temperature.  If  it  is 
necessary  for  the  body  to  rid  itself  of  an  excess  of  heat, 
the  quantity  of  blood  circulating  in  the  skin  is  increased. 
This  brings  the  blood  near  the  surface,  where  more  heat 
can  be  radiated  and  where  it  may  cause  an  increase  in  the 
perspiration.  On  the  other  hand,  if  the  body  is  in  danger 
of  losing  too  much  heat,  the  circulation  diminishes  in  the 
skin  and  increases  in  the  internal  organs.  This  stops  the 
rapid  loss  of  heat  from  the  surface.  The  skin  in  this  work 

1  Heat  also  leaves  the  body  by  the  lungs,  partly  by  the  respired  air  and  partly 
through  the  evaporation  of  moisture  from  the  lung  surfaces.  Respiration  in  some 
nnimals,  as  the  dog,  is  the  chief  means  of  cooling  the  body. 


THE    SKIN  271 

is  of  course  made  to  cooperate  with  other  parts  of  the  body. 
That  it  is  not  the  only  organ  concerned  in  regulating  the 
escape  of  heat  is  seen  in  the  results  that  follow  sensations 
either  of  chilliness  or  of  heat  at  the  surface. 

Effects  of  Heat  and  Cold  Sensations.  —  Sensations,  or 
feelings,  of  heat  and  cold  are  made  possible  through  the 
nerves  which  connect  the  brain  with  the  temperature 
corpuscles,  found  in  the  skin  (page  343).  As  the  warm 
blood  recedes  from  the  skin,  a  sensation  of  cold  is  felt, 
but  when  the  blood  returns,  there  is  again  the  feeling  of 
warmth.  The  sensation  of  cold  prompts  one  to  seek  a 
warmer  place,  or  to  put  on  more  clothing;  while  the  sensa- 
tion of  heat,  if  it  be  oppressive,  leads  to  activities  of  an 
opposite  kind.  Prompted  in  this  way  by  the  sensations  from 
the  skin,  one  voluntarily  supplies  the  external  conditions, 
such  as  clothing  and  heat,  that  affect  the  body  temperature. 

Alcohol  and  the  Regulation  of  Temperature.  —  Alcohol, 
through  its  effect  upon  the  nervous  system,  interferes  se- 
riously with  the  regulation  of  the  body  temperature.  By 
dilating  the  capillaries,  it  increases  the  circulation  in  the 
skin  and  leads  to  an  undue  loss  of  heat.  At  the  same 
time  the  excess  of  blood  in  the  skin  causes  a  feeling  of 
warmth  which  has  led  to  the  erroneous  belief  that  alcohol 
is  a  heat  producer.  If  taken  on  a  cold  day,  it  deceives 
one  about  his  true  condition  and  leads  to  a  wasting  of  heat 
when  it  should  be  carefully  economized.  Not  only  is 
alcohol  of  no  value  in  maintaining  the  body  temperature, 
but  if  taken  during  severe  exposure  to  cold,  it  becomes  a 
menace  to  life  itself.  Arctic  explorers  and  others  exposed 
to  severe  cold  have  found  that  they  withstand  cold  far 
better  when  no  alcohol  at  all  is  used.1 

1  "  The  story  is  told  of  some  woodsmen  who  were  overtaken  by  a  severe  snow- 
storm and  had  to  spend  the  night  away  from  camp  ;  they  had  a  bottle  of  whisky, 


272  COORDINATION   AND   SENSATION 

HYGIENE  OF   THE   SKIN 

Much  of  the  hygiene  of  the  skin  is  included  in  the 
problems  of  keeping  it  warm  and  clean.  It  is  kept  warm 
by  clothing ;  bathing  is  the  method  of  keeping  it  clean. 

Clothing  should  be  warm  and  loose-fitting.  Woolen 
fabrics  are  to  be  preferred  in  winter  to  cotton  because, 
being  poorer  conductors  of  heat,  they  afford  better  pro- 
tection from  the  cold.  But  wool  fails  to  absorb  the  per- 
spiration rapidly  from  the  skin  and  to  pass  it  to  the 
outside  where  it  is  evaporated.  This,  together  with  its 
tendency  to  irritate,  makes  woolen  clothing  somewhat 
objectionable  for  wearing  next  to  the  skin.  This  objec- 
tion, however,  is  obviated  by  woolen  underwear  which  is 
lined  by  a  thin  weaving  of  cotton. 

Bathing.  —  The  solid  material  from  the  perspiration, 
which  is  left  on  the  skin,  together  with  the  oil  from  the 
oil  glands  and  the  dirt  from  the  outside,  tends  to  close  up 
the  pores  and  develop  offensive  odors.  Keeping  the  skin 
clean  is,  for  these  reasons,  necessary  from  both  a  health 
and  a  social  standpoint.  While  one  should  always  keep 
clean,  the  frequency  of  the  bath  will  depend  upon  the 
season,  the  occupation  of  the  individual,  and  the  nature  and 
amount  of  the  perspiration.  As  to  the  kind  of  bath  to 
be  taken  and  the  precautions  to  be  observed,  no  specific 
rules  can  be  laid  down.  These  must  be  determined  by 

and,  chilled  to  the  bone,  some  imbibed  freely  while  others  refused  to  drink.  Those 
who  drank  soon  felt  comfortable  and  went  to  sleep  in  their  improvised  shelter ; 
those  who  did  not  drink  felt  very  uncomfortable  throughout  the  night  and  could 
get  no  sleep,  but  in  the  morning  they  were  alive  and  able  to  struggle  back  to  camp, 
while  their  companions  who  had  used  alcohol  were  frozen  to  death.  .  .  .  This,  if 
true,  was  of  course  an  extreme  case :  but  it  accords  with  the  universal  experience 
of  arctic  travelers  and  of  lumbermen  and  hunters  in  the  northern  woods,  that  the 
use  of  alcohol  during  exposure  to  cold,  although  contributing  greatly  to  one's 
comfort  for  the  time  being,  is  generally  followed  by  undesirable  or  dangerous 
results."  —  HOUGH  AND  SEDGWICK:  The  Elements  of  Hygiene  and  Sanitation. 


THE    SKIN 


2/3 


the  facilities  at  hand  and  by  the  health  and  natural  vigor 
of  the  bather.  Severe  chilling  of  the  body  should  be 
avoided,  especially  by  those  in  delicate  health.  If  a  hot 
bath  is  taken,  one  should  dash  cold  water  over  the  body 
on  finishing.  One  should  then  quickly  dry  and  rub  the 
body  with  a  coarse  towel.  The  dash  of  cold  water  closes 
the  pores  of  the  skin  and  lessens  the  liability  of  taking 
cold. 

The  Tonic  Bath.  —  The  cold  bath  has  been  found  to 
have  a  beneficial  effect  upon  the  general  health  beyond  its 
effect  upon  the  skin.  When  taken  with  care  as  to  the 
length  of  time  and  the  degree  of  cold,  decided  tonic  effects 
are  observed  on  the  circulation  and  on  the  nervous  system. 
The  rapid  changes  of  temperature  vigorously  exercise  the 
non-striated  muscles  of  the  bloodvessels  (page  57)  and  the 
nerves  controlling  them.  The  irritability  of  the  nervous 
system  in  general  is  also  lessened.  For  this  reason  the 
cold  bath  is  one  of  the  best  means  of  keeping  both  mind 
and  body  in  good  condition  during  the  warm  months. 
Sponging  off  the  body  with  cold  or  tepid  water  before 
retiring  is  also  an  excellent  aid  in  securing  sound  sleep 
during  the  hot  summer  nights. 

Danger  from  the  cold  bath  arises  through  the  shock  to 
the  nervous  system  and  the  loss  of  heat  from  the  body. 
It  is  avoided  by  using  water  whose  temperature  is  not  too 
low  and  by  limiting  the  time  spent  in  the  bath.  A  brisk 
rubbing  with  a  coarse  towel  should  always  follow  the  cold 
bath.  People  past  middle  age  are,  as  a  rule,  not  benefited 
by  the  cold  bath ;  and  those  in  delicate  health,  especially 
if  inclined  toward  rheumatism,  are  likely  to  be  affected 
injuriously  by  it. 

Care  of  the  Complexion.  —  A  good  complexion  is  a  natu- 
ral accompaniment  of  good  health  and  depends  primarily 


274  COORDINATION    AND    SENSATION 

upon  two  conditions  —  a  clear  skin  and  an  active  circula- 
tion of  the  blood  through  it.  Clearness  of  the  skin  de- 
pends largely  upon  the  elimination  of  waste  material  from 
the  body,  and  where  the  solid  wastes  are  not  effectively  re- 
moved through  the  natural  channels  (the  liver,  kidneys, 
and  bowels),  blotches,  sallowness  of  the  skin,  and  skin 
eruptions  are  likely  to  result.  In  seeking  to  clear  the 
complexion,  attention  must  be  given  to  all  those  agencies 
that  favor  the  elimination  of  waste,  and  especially  should 
there  be  a  free  and  thorough  evacuation  of  the  bowels  each 
day.  The  general  health  should  also  be  looked  after, 
attention  being  given  to  exercise,  fresh  air,  proper  food,1 
sufficient  sleep,  etc. 

Bathing  is  the  chief  means  employed  for  increasing  the 
circulation  in  the  skin,  although  exercise  which  is  suf- 
ficiently vigorous  to  cause  one  to  perspire  freely  is  a  valu- 
able aid.  A  daily  bath  of  warm  or  hot  water,  finished  off 
with  a  dash  of  cold,  followed  by  a  thorough  rubbing  of 
the  entire  surface,  and  this  by  a  kneading  of  the  skin  with 
the  thumbs  and  fingers,  will  in  most  cases  bring  about  the 
desired  results.  A  little  olive  oil,  thoroughly  worked  into 
the  skin  during  the  kneading  process,  is  beneficial  where 
one  lacks  flesh  or  where  the  skin  is  dry  and  thin.  The 
olive  oil  is  also  beneficial  where  the  baths  are  exhausting  or 
render  one  susceptible  to  cold.  In  rubbing  and  kneading, 
the  skin  should  not  be  bruised  or  irritated. 

The  much  advertised  "complexion  beautifiers "  which 
are  applied  directly  to  the  face  frequently  have  the  effect 
of  clogging  the  pores  and  of  causing  eruptions  of  the  skin. 

1  Foods  that  are  difficult  to  digest,  or  which  cause  disturbances  of  the  digestive 
organs  (a  coated  tongue  being  one  indication),  have  a  bad  effect  upon  the  skin. 
It  is  in  this  way  that  the  use  of  tea  and  coffee  by  some  people  induces  a  sallow  or 
"muddy"  condition  of  the  complexion. 


THE    SKIN  275 

On  the  other  hand,  certain  authorities  state  that  the  cold 
cream  preparations  may  be  of  advantage  in  giving  the 
skin  a  desired  softness,  and  that  when  judiciously  used 
(the  face  being  cleansed  after  each  application)  they  do 
no  harm.  Of  the  different  kinds  of  face  powder  those 
prepared  from  rice  are  considered  the  least  injurious. 

Treatment  of  Skin  Wounds.  —  Skin  wounds  which 
may  not  be  serious  in  themselves  frequently  become  so 
through  getting  infected  with  germs.  Blood  poisoning 
often  results  from  such  infections,  one  of  the  worst  forms 
being  tetanus,  or  lockjaw.  A  wound  should  be  kept  clean, 
and  if  it  shows  signs  of  infection,  it  should  be  washed  with 
some  antiseptic  solution.  Or,  it  may  be  cleansed  with  pure 
warm  water  and  then  covered  with  some  antiseptic  oint- 
ment,1 of  which  there  are  a  number  on  the  market.  A  weak 
solution  of  carbolic  acid  (one  part  acid  to  twenty-five  parts 
of  water)  makes  an  excellent  antiseptic  wash.  It  may  be 
used  not  only  for  cleansing  wounds,  but  also  in  counter- 
acting the  poisonous  effects  that  follow  the  bites  of  insects. 

A  wound  resulting  from  the  bite  of  an  animal  (cat  or 
dog),  even  though  slight,  should  receive  more  serious 
attention,  and  as  soon  as  possible  after  the  occurrence. 
Such  wounds  should  be  cauterized,  and  for  this  purpose 
pure  carbolic  acid  (undiluted  with  water)  may  be  used.  A 
wooden  toothpick  is  dipped  into  the  acid  and  this  is 
worked  about  in  the  wound.  The  acid  is  then  washed  out 
with  warm  water.  A  deep  wound  from  a  rusty  nail  or 

1 A   most  valuable  antiseptic  ointment  is  prepared  by  the  druggist  from  the 

following  formula  : 

Lanolin,  25  grams. 

Ichthyol,  6  grams. 

Yellow  vaseline,         20  grams. 

This  is  applied  as  a  thin  layer  on  the  surface,  except  in  the  case  of  boils  or 
abscesses.  In  treating  these  a  heavy  layer  is  spread  over  the  affected  part  and 
then  covered  witfi  absorbent  cotton  or  a  thin  piece  of  clean  cotton  cloth. 


276  COORDINATION   AND   SENSATION 

a  thorn  should  be  treated  in  the  same  manner  and  should 
be  kept  open,  not  being  allowed  to  heal  at  the  surface  first. 
If  one  has  reason  to  believe  he  has  been  bitten  by  a  mad 
dog,  the  wound  should  be  cauterized  as  above,  and  a  physi- 
cian should  be  summoned  at  once.  Deep  wounds  from  ex- 
plosives, or  other  causes,  should  also  receive  the  attention 
of  the  physician.  Many  cases  of  lockjaw  result  every  year 
from  wounds  inflicted  by  the  toy  pistols,  firecrackers,  etc., 
used  in  our  Fourth  of  July  celebrations.  These  are  due  to 
the  embedding  in  the  skin  or  flesh  of  small  solid  particles 
on  which  are  lockjaw  germs.  Wounds  of  this  nature 
should,  of  course,  receive  the  attention  of  the  physician. 
Care  of  the  Nails.  —  Relief  from  a  blood  blister  under 
the  nail  is  secured  by  boring  a  small  hole  through  the  nail 
with  the  sharp  point  of  a  sterilized  penknife 
(page  38).  This  simple  bit  of  surgery  not 
only  relieves  the  pain,  but  is  frequently  the 
only  means  of  saving  the  nail.  Ingrown  toe 
FIG.  124^—  nails  are  relieved  by  scraping  a  broad  strip 
Proper  method  in  the  middle  of  the  nail  until  very  thin, 
of  trimming  This  relieves  the  pressure,  preventing  the 
sides  of  the  nail  from  being  forced  into  the 
toe.  While  the  finger  nails  should  be  trimmed  in  a  curve, 
corresponding  to  the  end  of  the  finger,  it  is  recommended 
that  the  toe  nails  be  cut  straight  across  (Fig.  124),  as  this 
method  diminishes  the  pressure  from  the  shoe  and  keeps 
the  nails  from  ingrowing.  Shoes  that  pinch  the  toes 
should,  of  course,  not  be  worn  (page  238). 

Care  of  the  Hair.  —  Occasional  washing  of  the  hair  is 
beneficial,  but  too  much  wetting  causes  decay  of  the  hair 
roots,  which  leads  to  its  falling  out.  The  worst  enemy  of 
the  hair  is  dandruff.  A  method  of  removing  dandruff 
which  is  highly  recommended  is  that  of  rubbing  olive  oil 


THE   SKIN  277 

into  the  scalp  and  later  of  removing  this  with  a  cleansing 
shampoo.  The  olive  oil  is  placed  on  the  scalp  with  a  medi- 
cine dropper  and  thoroughly  rubbed  in  with  the  fingers. 
After  three  or  four  hours  the  hair  is  washed  with  soap 
and  water  (any  good  toilet  soap  will  do)  and  rinsed  with 
pure  water.  The  hair  is  then  dried,  the  surplus  water  being 
removed  with  a  coarse  towel.  Where  the  dandruff  is  very 
troublesome,  this  treatment  may  be  given  once  or  twice  a 
week ;  but  in  mild  cases  once  a  month  is  sufficient.  Massage 
of  the  scalp,  by  increasing  the  circulation  at  the  hair  roots,  is 
beneficial,  but  irritation  by  a  fine-tooth  comb,  a  stiff  hair 
brush,  or  by  other  means  should  be  avoided.  Frequent 
brushing  and  combing,  however,  are  necessary  both  for 
the  good  appearance  of  the  hair  and  for  spreading  the  oil 
secreted  by  the  glands  at  the  hair  roots. 

Summary.  —  The  skin  forms  the  external  covering  of 
the  body  and  also  serves  additional  purposes.  It  is  a  most 
important  agency  in  adapting  the  body  to  its  physical  sur- 
roundings, as  shown  by  the  part  which  it  plays  in  the  regu- 
lation of  the  body  temperature.  The  skin  should  be  kept 
clean  and  active,  and  skin  wounds,  even  though  small, 
should  be  guarded  against  infection. 

Exercises.  —  i.  Name  an  example  of  each  of  the  protective  coverings 
of  the  body. 

2.  Compare  the  dermis  and  the  epidermis  with  reference  to  thick- 
ness, composition,  and  function. 

3.  To  what  is  the  color  of  the  skin  due  ?     How  is  the  color  of  the 
skin  affected  by  the  sunlight  ? 

4.  What  modifications  of  the  epidermis  are  found  on  our  bodies  ? 
What  are  found  on  the  body  of  a  chicken  ? 

5.  What  different  kinds  of  protection  are  provided  by  the  skin  ? 

6.  How  does  the  perspiration  cool  the  body  ? 

7.  What  change  occurs  in  the  circulation  in  the  skin  when  the  body 
is  becoming  too  cold  ?     When  becoming  too  warm  ?     What  is  the  pur- 
pose of  these  changes  ? 


278  COORDINATION    AND   SENSATION 

8.  How  does  alcohol  cause  one  to  feel  warm  when  he  may  be  losing 
too  much  of  his  heat  ? 

9.  What  precaution  should  be  observed  by  one  in  poor  health,  in 
taking  a  bath  ? 

10.  How  may  the  cold  bath  be  a  means  of  improving  the  general 
health  ? 

PRACTICAL  WORK 

Observations  on  the  Skin  and  its  Appendages.  —  Examine  the  palm  of 
the  hand  with  a  lens.  Note  the  small  ridges  which  correspond  to  the 
rows  of  papillae  beneath  the  cuticle.  In  these  find  small  pits,  which  are 
the  openings  of  the  sweat  glands. 

2.  Examine  the  epidermis  on  the  back  of  the  hand  and  palm.     At 
which  place  is  it  thickest  and  most  resisting  ?     Is  it  of  uniform  thick- 
ness over  the  palm  ?     Try  picking  it  with  a  pin  at  the  thickest  place, 
noting  if  pain  is  felt.     Inference  ? 

3.  Examine  a  finger  nail.     Is  the  free  edge  or  the  root  the  thickest  ? 
Trim  closely  the  thumb  nail  and  the  nail  of  the  middle  finger  of  one 
hand  and  try  to  pick  up  a  pin,  or  other  minute  object,  from  a  smooth, 
hard  surface.     The  result  indicates  what  use  of  the  nails  ?     Suggest 
other  uses. 

4.  Examine  with  a  microscope  under  a  low  power  hairs  from  a 
variety  of  animals,  as  the  horse,  dog,  cat,  etc.,  noting  peculiarities  of 
form  and  surface. 

To  illustrate  Cooling  Effects  of  Evaporation.  —  i.  Wet  the  back  of 
the  hand  and  move  it  through  the  air  to  hasten  evaporation.  Observe 
that,  as  the  hand  dries,  a  sensation  of  cold  is  felt.  Repeat  the  experi- 
ment, using  ether,  alcohol,  or  gasolene  instead  of  the  water,  noting  the 
difference^  in  results.  These  liquids  evaporate  faster  than  water. 

2.  Wet  the  bulb  of  a  thermometer  with  alcohol  or  water.  Move  it 
through  the  air  to  hasten  evaporation.  Note  and  account  for  the  fall 
of  the  mercury. 


CHAPTER   XVII 
STRUCTURE   OF  THE  NERVOUS  SYSTEM 

Coordination  and  Adjustment.  —  If  we  consider  for  a 
moment  the  movements  of  the  body,  we  cannot  fail  to 
note  the  cooperation  of  organs,  one  with  another.  In  the 
simple  act  of  whittling  a  stick  one  hand  holds  the  stick  and 
the  other  the  knife,  while  the  movements  of  each  hand  are 
such  as  to  aid  in  the  whittling  process.  Examples  of  co- 
operation are  also  found  in  the  taking  of  food,  in  walking, 
and  in  the  performance  of  different  kinds  of  work.  Not 
only  is  cooperation  found  among  the  external  organs,  but 
our  study  of  the  vital  processes  has  shown  that  the  princi- 
ple of  cooperation  is  carried  out  by  the  internal  organs  as 
well.  The  fact  that  all  the  activities  of  the  body  are 
directed  toward  a  common  purpose  makes  the  cooperation 
of  its  parts  a  necessity.  The  term  "  coordination  "  is  em- 
ployed to  express  this  cooperation,  or  working  together,  of 
the  different  parts  of  the  body. 

A  further  study  of  the  movements  of  the  body  shows 
that  many  of  them  have  particular  reference  to  things  out- 
side of  it.  In  going  about  one  naturally  avoids  obstruc- 
tions, and  if  anything  is  in  the  way  he  walks  around  or 
steps  over  it.  Somewhat  as  a  delicate  instrument  (the 
microscope  for  example)  is  altered  or  adjusted,  in  order  to 
adapt  it  to  its  work,  the  parts  of  the  body,  and  the  body 
as  a  whole,  have  to  be  adjusted  to  their  surroundings. 
This  is  seen  in  the  attitude  assumed  in  sitting  and  in 
standing,  in  the  position  of  the  hands  for  different  kinds 

279 


280  COORDINATION    AND   SENSATION 

of  work,  in  the  variations  of  the  circulation  of  the  blood  in 
the  skin,  and  in  the  movements  for  protecting  the  body.1 
Work  of  the  Nervous  System.  —  How  are  the  different 
activities  of  the  body  controlled  and  coordinated?  How 
is  the  body  adjusted  to  its  surroundings?  The  answer  is 
found  in  the  study  of  the  nervous  system.  Briefly  speak- 
ing, the  nervous  system  controls,  coordinates,  and  adjusts 
the  different  parts  of  the  body  by  fulfilling  two  conditions : 

1.  It    provides    a    complete    system     of     connections 
throughout  the  body,  thereby  bringing  all  parts  into  com- 
munication. 

2.  It  supplies  a  means  of  controlling  action  (the  so-called 
impulse)  which  it  passes  along  the  nervous  connections 
from  one  part  of  the  body  to  another. 

The  present  chapter  deals  with  the  first  of  these  condi- 
tions; the  chapter  following,  with  the  second. 

The  Nerve  Skeleton.  —  If  all  the  other  tissues  are  re- 
moved, leaving  only  the  nervous  tissue,  a  complete  skele- 
ton outline  of  the  body  still  remains.  This  nerve  skeleton, 
as  it  has  been  called,  has  the  general  form  of  the  framework 
of  bones,  but  differs  from  it  greatly  in  the  fineness  of  its 
structures  and  the  extent  to  which  it  represents  every 
portion  of  the  body.  An  examination  of  a  nerve  skeleton, 
or  a  diagram  of  one  (Fig.  125),  shows  the  main  structures 
of  the  nervous  system  and  their  connection  with  the  dif- 
ferent parts  of  the  body. 

Corresponding  to  the  skull  and  the  spinal  column  is 
a  central  nervous  axis,  made  up  of  two  parts,  the  brain  and 
the  spinal  cord.  From  this  central  axis  white,  cord-like 
bodies  emerge  and  pass  to  different  parts  of  the  body. 

1  In  a  larger  sense  adjustment  includes  all  those  activities  by  means  of  which 
the  body  is  brought  into  proper  relations  with  its  environment,  including  the 
changes  which  the  body  makes  in  its  surroundings  to  adapt  them  to  its  purposes. 


STRUCTURE   OF   THE   NERVOUS    SYSTEM 


28l 


These  are  called  nerve  trunks,  and  the  smaller  branches 
into  which  they  divide  are  called  nerves.  The  nerves  also 
undergo  division  until  they 
terminate  as  fine  thread-like 
structures  in  all  parts  of  the 
body.  The  distribution  of 
nerve  terminations,  however, 
is  not  uniform,  as  might  be 
supposed,  but  the  skin  and  im- 
portant organs  like  the  heart, 
stomach,  and  muscles  are  the 
more  abundantly  supplied. 
On  many  of  the  nerves  are 
small  rounded  masses,  called 
ganglia,  and  from  many  of 
these  small  nerves  also  emerge. 
At  certain  places  the  nerves 
and  ganglia  are  so  numerous 
as  to  form  a  kind  of  network, 
known  as  a  plexus. 

It  is  through  these  struc- 
tures— brain  and  spinal  cord, 
nerve  trunks  and  nerves,  gan- 
glia and  nerve  terminations 
— that  connections  are  estab- 
lished between  all  parts  of  the 
body,  but  more  especially  be- 
tween the  surface  of  the  body 
and  the  organs  within.  FIG.  125.  —  Diagram  of  nerve 

The  Neurons,  or  Nerve  Cells,  skeleton.    The  illustration  shows 

-While  a   hasty  examination    the  extent  and  general  arrangement 
J  of  the  nervous   tissue.       A.  Brain. 

of  the  nerve  skeleton  is  suffi-  B  Spinal  cord      ^  Nerve  trunks 

Cient   to    show   the  connection    and  nerves.     G.  Ganglia. 


282 


COORDINATION   AND    SENSATION 


of  the  nervous  system  with  all  parts  of  the 
body,  no  amount  of  study  of  its  gross  struc- 
tures reveals  the  nature  of  its  connections 
or  suggests  its  method  of  operation.  In- 
sight into  the  real  nature  of  the  nervous 
systern  is  obtained  only  through  a  study  of 
its  minute  structural  elements.  These,  in- 
stead of  being  called  cells,  a*s  in  the  case  of 
the  other  tissues,  are  called  neurons.  The 
use  of  this  term,  instead  of  the  simpler  one 
of  nerve  cell,  is  the  result  of  recent  ad- 
vances in  our  knowledge  of  the  nervous 
system.1 

The  neurons  are  in  all  respects  cells. 
They  differ  widely,  however,  from  all  the 
other  cells  of  the  body  and  are,  in  some 
respects,  the  most  remarkable  of  all  cells. 
j       •     ,  They  are  characterized  by  minute  exten- 
branches  sions,  or  prolongations,  which  in  some  in- 
J\^  stances  extend  to  great  distances.    Though 

'  ,      T..      the  neurons  in  certain  parts  of  the  body 
tic.  1  20.  —  Dia-  f  J 

gram  of  a  mon-ax-  differ  greatly  in  form  and  size  from  those 
onic  neuron  (great-  in  other  parts  of  the  body,  most  of  them 
ly  enlarged  except  as  may  be  inciuded  in  one  or  the  other  of 

to  length).  Thecen-  .  . 

...        ,   .     .,     two  classes,  known  as  mon-axonic  neurons 

tral    thread    in    the 

axon  is  the  axis  cyl-  and  di-cixonic  neurons. 

Mon-axonic  Neurons.  —  Neurons  of  this 


III  b 


1  Almost  to  the  present  time,  physiologists  have  described  the  nervous  system  as 
being  made  up  of  two  kinds  of  structural  elements  which  were  called  nerve  cells 
and  nerve  fibers.  The  nerve  cells  were  supposed  to  form  the  ganglia  and  the  fibers 
to  form  the  nerves.  Recent  investigators,  however,  employing  new  methods  of 
microscopic  study,  have  established  the  fact  that  the  so-called  nerve  cell  and  nerve 
fiber  are  but  two  divisions  of  the  same  thing  and  that  the  nervous  system  is  made  up 
of,  not  two,  but  one  kind  of  structural  element  The  term  "neuron"  is  used  to 
denote  this  structural  element,  or  complete  nerve  cell. 


STRUCTURE    OF   THE    NERVOUS    SYSTEM          283 

class  consist  of  three  distinct  parts,  known  as  the  cell-body, 
the  dendrites,  and  the  axon  (Fig.  126). 

The  cell-body  has  in  itself  the  form  of  a  complete  cell 
and  was  at  one  time  so  described.  It  consists  of  a  rounded 
mass  of  protoplasm,  containing  a  well-defined  nucleus. 
The  protoplasm  is  similar  to  that  of  other  cells,  but  is 
characterized  by  the  presence  of  many  small  granules  and 
has  a  slightly  grayish  color. 

The  dendrites  are  short  extensions  from  the  cell-body. 
They  branch  somewhat  as  the  roots  of  a  tree  and  form  in 
many  instances  a  complex  network  of  tiny  rootlets.  Their 
protoplasm,  like  that  of  the  cell-body,  is  more  or  less 
granular.  The  dendrites  increase  greatly  the  surface  of 
the  cell-body,  to  which  they  are  related  in  function. 

The  axon,  or  nerve  fiber,  is  a  long,  slender  extension 
from  the  cell-body,  which  connects  with  some  organ  or 
tissue.  It  was  at  one  time  described  as  a  distinct  nervous 
element,  but  later  study  has  shown  it  to  be  an  outgrowth 
from  the  cell-body.  The  mon-axonic  neurons  are  so 
called  from  their  having  but  a  single  axon. 

Di-axonic   Neurons.  —  Neurons   belonging   to  this 
class    have   each    a   well-defined   cell-body   and   two 

axons,    but    no 

ody  TK%&*^   parts     just     like 

the  dendrites   of 

FIG.    127. -Diagram    of    a    di-axonic   mon.axonic    neu- 
neuron.     The  diagram  shows  only  the  con-  _,,  .. 

ducting  portion  of  the  axon,  or  axis  cylinder. 

body    is    smooth 

and  rounded,  and  its  axons  extend  from  it  in  opposite  di- 
rections (Fig.  127). 

Structure  of  the  Axon. — The  axon,  or  nerve  fiber,  has 
practically  the  same  structure  in  both  classes  of  neurons, 
being  composed  in  most  cases  of  three  distinct  parts.  In 


284  COORDINATION    AND    SENSATION 

the  center,  and  running  the  entire  length  of  the  axon,  is  a 
thread-like  body,  called  the  axis  cylinder  (Fig.  126).  The 
axis  cylinder  is  present  in  all  axons  and  is  the  part  essential 
to  their  work.  It  may  be  considered  as  an  extension  of 
the  protoplasm  from  the  cell-body.  Surrounding  the  axis 
cylinder  is  a  thick,  whitish-looking  layer,  known  as  the 
medullary  sheath,  and  around  this  is  a  thin  covering,  called 
fas  primitive  sheath,  or  neurilemma.  The  medullary  sheath 
and  the  primitive  sheath  are  not,  strictly  speaking,  parts  of 
the  nerve  cell,  but  appear  to  be  growths  that  have  formed 
around  it.  Certain  of  the  axons  have  no  primitive  sheath 
and  others  are  without  a  medullary  sheath.1 

Form  and  Length  of  Axons.  —  Where  the  axons  terminate  they  usually 
separate  into  a  number  of  small  divisions,  thereby  increasing  the  number 
of  their  connections.  Certain  axons  are  also  observed  to  give  off 
branches  before  the  place  of  termination  is  reached  (Fig.  131).  These 
collateral  branches,  by  distributing  themselves  in  a  manner  similar  to 
the  main  fiber,  greatly  extend  the  influence  of  a  single  neuron. 

In  the  matter  of  length,  great  variation  is  found  among  the  axons  in 
different  parts  of  the  body.  In  certain  parts  of  the  brain,  for  example, 
are  fibers  not  more  than  one  one-hundredth  of  an  inch  in  length,  while 
the  axons  that  pass  all  the  way  from  the  spinal  cord  to  the  toes  have 
a  length  of  more  than  three  feet.  Between  these  extremes  practically 
all  variations  in  length  are  found. 

Arrangements  of  the  Neurons.  —  Nowhere  in  the  body 
do  the  neurons  exist  singly,  but  they  are  everywhere 
connected  with  each  other  to  form  the  different  structures 
observed  in  the  nerve  skeleton.  Two  general  plans  of 
connection  are  to  be  observed,  known  as  the  anatomical 
and  the  physiological,  or,  more  simply  speaking,  as  the 
"side-by-side"  and  "end-to-end"  plans.  The  side-by- 

1  Many  of  the  axons  in  the  brain  and  spinal  cord  have  no  primitive  sheath. 
Axons  without  the  medullary  sheath  are  found  in  the  sympathetic  nerves.  These 
are  known  as  non-medullated  axons  and  they  have  a  gray  instead  of  a  white  color. 


STRUCTURE   OF   THE   NERVOUS    SYSTEM 


285 


side  plan  is  seen  in  that  disposition  of  the  neurons  which 
enables  them  to  form  the  nerves  and  the  ganglia,  as  well 
as  the  brain  and  spinal  cord.  The  end-to-end  connections 
are  necessary  to  the  work  which  the  neurons  do. 

Side-by-side  Connections.  —  On  separating  the  ganglia 
and  nerves  into  their  finest  divisions,  it  is  found  that  the 
nerves  consist  of  axons,  while  the  ganglia  are  made  up 
mainly  of  cell-bodies  and  dendrites.  The  axons  lie  side 


FIG.  1 28.  —  Diagrams  illustrating  arrangement  of  neurons.  A,  B.  Gan- 
glia and  short  segments  of  nerves.  I.  Ganglion.  2.  Nerve.  In  the  ganglion 
of  A  are  end-to-end  connections  of  different  neurons;  in  the  ganglion  of  B 
are  the  cell-bodies  of  di-axonic  neurons.  C.  Section  of  a  nerve  trunk. 
I.  Epineurium  consisting  chiefly  of  connective  tissue.  2.  Bundles  of  nerve 
fibers.  3.  Covering  of  fiber  bundle,  or  perineurium.  4.  Small  artery  and 
vein. 

by  side  in  the  nerve,  being  surrounded  by  the  same  pro- 
tective coverings,  while  the  cell-bodies  form  a  rounded 
mass  or  cluster,  which  is  the  ganglion  (Fig.  128).  But  the 
axons,  in  order  to  connect  with  the  cell-bodies,  must  termi- 
nate within  the  ganglion,  so  that  they  too  form  a  part  of  it. 
To  some  extent,  also,  axons  pass  through  ganglia  with  which 
they  make  no  connection.  The  neurons  in  the  brain  and 
spinal  cord  also  lie  side  by  side,  but  their  arrangement  is 
more  complex  than  that  in  the  nerves  and  ganglia. 


286 


COORDINATION    AND    SENSATION 


The  side-by-side  arrangement  of  the  neurons  shows  clearly  the  struc- 
ture of  the  ganglia  and  nerves.  The  nerve  is  seen  to  be  a  bundle 
of  axons.  or  nerve  fibers,  held  together  by  connective  tissue,  while  the 
ganglion  is  little  more  than  a  cluster  of  cell-bodies.  Their  connection 
is  necessarily  very  close,  for  the  same  group  of  neurons  will  form,  with 
their  axons,  the  nerve,  and,  with  their  cell-bodies,  the  ganglion  (Fig. 
128). 

End-to-end  Connections.  —  These  consist  of  loose  end-to- 
end  unions  of  the  fiber  branches  of  certain  neurons  with 


Muscle 
cell 


Spinal  cord. 

'  ' 


Skin 


FIG.  129.  —  Diagram  of  a  nerve  path  starting  at 
the  skin,  extending  through  the  spinal  cord,  and  pass- 
ing out  to  muscles.  A  division  of  this  path  also 
reaches  the  brain. 


the  dendrites  of  other  neurons.  The  pur- 
pose of  such  connections  is  to  provide  the 
means  of  communication  between  different 
parts  of  the  body.  There  appears  to  be 
no  actual  uniting  of  the  fiber  branches  with  the  dendrites, 
but  they  come  into  relations  sufficiently  close  to  establish 
conduction  pathways,  and  these  extend  throughout  the  body 
(Fig.  129).  They  connect  all  parts  of  the  body  with  the 
brain  and  spinal  cord,  while  connections  within  the  brain 
and  cord  bring  the  parts  into  communication  with  each 
other. 


STRUCTURE   OF   THE   NERVOUS   SYSTEM 


287 


Nature  of  the  Nervous  System.  —  The  nervous  system 
represents  the  sum  total  of  the  neurons  in  the  body.  In 
some  respects  it  may  be  compared  to  the  modern  telephone 
system.  The  neurons,  like  the  electric  wires,  connect  dif- 
ferent places  with  a  central  station  (the  brain  and  spinal 
cord),  and  through  the  central  station  connections  are 
established  between  the  different  places  in  the  system. 
As  the  separate  wires  are  massed  together  to  form  cables, 
the  neurons  are  massed  to  form  the  gross  structures  of 
the  nervous  system.  The  nervous  system,  however,  is  so 
radically  different  from  anything  found  outside  of  the  ani- 
mal body  that  no  comparison  can  give  an  adequate  idea  of 
it.  We  now  pass  to  a  study  of  the  gross  structures  ob- 
served in  the  nerve  skeleton. 

Divisions  of  the  Nervous  System. — While  all  of  the 
nervous  structures  are  very  closely  blended,  forming  one 
complete  system  for  the  entire  body,  this  system  presents 
different  divisions  which  may,  for  convenience,  be  studied 
separately.  As  physiologists  have  become  better  ac- 
quainted with  the  human  nervous  system,  different  schemes 
of  classification  have  been  proposed.  The  following  out- 
line, based  upon  the  location  of  the  different  parts,  presents 
perhaps  the  simplest  view  of  the  entire  group  of  nervous 

structures : 

(Forebrain  —  Cerebrum 
Midbrain 
TPons 
_  Hindbrain  -  Cerebellum 

(Bulb 

Spinal  cord 
Nervous  System  r  Dorsal-root  ganglia 


Brain 


Peripheral 


in*  '    (Sympathetic  ganglia 

(Cranial  nerves 
Nerves  J  Spinal  nerves 

I  Sympathetic  nerves 


288  COORDINATION    AND    SENSATION 

The  Central  Division.  —  This  division  of  the  nervous  sys- 
tem lies  within  the  cranial  and  spinal  cavities,  and  consists 
of  the  brain  and  the  spinal  cord.  The  brain  occupying 
the  cranial  cavity  and  the  spinal  cord  in  the  spinal  cavity 
connect  with  each  other  through  the  large  opening  at  the 
base  of  the  skull  to  form  one  continuous  structure.  The 
brain  and  cord  are  the  most  complicated  portions  of  the 
nervous  system,  and  the  ones  most  difficult  to  understand. 
The  Brain.  —  The  brain,  which  is  the  largest  mass  of 
nervous  tissue  in  the  body,  weighs  in  the  average  sized 

man  about  50  ounces,  and  in 
the  average  sized  woman  about 
44  ounces.1  It  may  be  roughly 
divided  into  three  parts,  which 
are  named  from  their  positions 
(in  lower  animals)  the  forebrain, 

bellum     x  ....... 

the  midbram,  and  the  hindbram 

f        (Fig.   130).     The   forebrain   con- 
FIG.  130.  —  Diagram  of 

divisions  of  brain.  sists  almost  entirely  of  a  single 

part,  known  as 

The  Cerebrum.  —  The  cerebrum  comprises  about  seven 
eighths  of  the  entire  brain,  and  occupies  all  the  front, 
middle,  back,  and  upper  portions  of  the  cranial  cavity, 
spreading  over  and  concealing,  to  a  large  extent,  the  parts 
beneath.  The  surface  layer  of  the  cerebrum  is  called  the 
cortex.  This  is  made  up  largely  of  cell-bodies,  and  has  a 
grayish  appearance.2  The  cortex  is  greatly  increased  in 

1  The  difference  in  weight  between  the  brain  of  man  and  that  of  woman  is  due 
mainly  to  the  fact  that  man's  body  is,  as  a  rule,  considerably  larger  than  that  of 
woman's. 

2  The  nervous  tissues  present,  at  different  places,  two  colors —  one  white,  and 
the  other  a  light  gray.     Great  significance  was  formerly  attached  to  these  colors, 
because  it  was  supposed  that  they  represented  two  essentially  different  kinds  of 
nervous  matter.     It  is  now  known  that  the  protoplasm  in  all  parts  of  the  neuron 


STRUCTURE   OF   THE   NERVOUS   SYSTEM 


289 


area  by  the  presence  everywhere  of  ridge-like  convolutions, 
between  which  are  deep  but  narrow  depressions,  called 
fissures.  The  interior  of  the 
cerebrum  consists  mainly  of 
nerve  fibers,  or  axons,  which  give 
it  a  whitish  appearance.  These 
fibers  connect  with  the  cell- 
bodies  in  the  cortex  (Fig.  131). 

The  cerebrum  is  a  double 
organ,  consisting  of  two  similar 
divisions,  called  the  cerebral 
hemispheres.  These  are  sepa- 
rated by  a  deep  groove,  extend- 
ing from  the  front  to  the  back 
of  the  brain,  known  as  the 
median  fissure.  The  hemi- 
spheres, however,  are  closely 
connected  by  a  great  band  of 
underlying  nerve  fibers,  called 
the  corpus  callosum. 

At  the  base  of  the  cerebrum  three  FlG- 131-  —  Microscope  draw- 
large  masses  of  cell-bodies  are  to  be  »»g  °f  a  neuron  from  cerebral 
found.  One  of  these,  a  double  mass,  cortex-  *•  short  *egment  °f 
occupies  a  central  position  between  the  the  axis  c>'linder  with  collateral 
hemispheres,  and  is  called  the  optic  branches- 

thalami.  The  other  two  occupy  front  central  positions  at  the  base  of 
either  hemisphere,  and  are  known  as  the  corpora  striata,  or  the  striate 
bodies. 

The  Midbrain  is  a  short,  rounded,  and  compact  body 
that  lies  immediately  beneath  the  cerebrum,  and  connects 

proper  — cell-body,  axis  cylinder,  and  dendrites  —  has  a  grayish  color,  while  the 
coverings  of  most  of  the  fibers  are  white.  Hence  gray  matter  in  any  part  of  the 
nervous  system  indicates  the  presence  of  cell-bodies,  and  white  matter  the  presence 
of  nr rve  fibers. 


290 


COORDINATION   AND   SENSATION 


it  with  the  hindbrain.  On  account  of  the  great  size  of  the 
cerebrum,  the  midbrain  is  entirely  concealed  from  view 
when  the  other  parts  occupy  their  normal  positions.  How- 
ever, if  the  cerebrum  is  pulled  away  from  the  hindbrain, 
it  is  brought  into  view  somewhat  as  in  Fig.  1 30. 

The  midbrain  carries  upon  its  back  and  upper  surface  four  small 
rounded  masses  of  cell-bodies,  called  the  corpora  quadrigemina.  The 
upper  two  of  these  bodies  are  connected  with  the  eyes  ;  the  lower  two 
appear  to  have  some  connection  with  the  organs  of  hearing.  On  the 
front  and  under  surface,  the  midbrain  separates  slightly  as  if  to  form 
two  pillars,  which  are  called  the  crura  cerebri,  or  cerebral  peduncles. 
These  contain  the  great  bundles  of  nerve  fibers  that  connect  the  cere- 
brum with  the  parts  of  the  nervous  system  below. 

The  Hindbrain  lies  beneath  the  back  portion  of  the 
cerebrum,  and  occupies  the  enlargement  at  the  base  of  the 
skull.  It  forms  about  one  eighth  of  the  entire  brain,  and 
is  composed  of  three  parts  —  the  cerebellum,  the  pons, 
and  the  bulb. 

The  Cerebellum  is  a  flat  and  somewhat  triangular  struc- 
ture with  its  upper  surface  fitting  into  the  triangular  under 
surface  of  the  back  of  the  cerebrum.  .  It  is  divided  into 
three  lobes  —  a  central  lobe  and  two  lateral  lobes  —  and 
weighs  about  two  and  one  half  ounces.  In  its  general 
form  and  appearance,  as  well  as  in  the  arrangement  of  its 
cell-bodies  and  axons,  the  cerebellum  resembles  the  cere- 
brum. It  differs  from  the  cerebrum,  however,  in  being 
more  compact,  and  in  having  its  surface  covered  with  nar- 
row, transverse  ridges  instead  of  the  irregular  and  broader 
convolutions  (Fig.  132). 

The  Pons,  or  pons  Varolii,  named  from  its  supposed  re- 
semblance to  a  bridge,  is  situated  in  front  of  the  cerebel- 
lum, and  is  readily  recognized  as  a  circular  expansion  which 
extends  forward  from  that  body.  It  consists  largely  of 


STRUCTURE   OF   THE   NERVOUS   SYSTEM          291 

bands  of  nerve  fibers,  between  which  are  several  small 
masses  of  cell-bodies.  The  fibers  connect  with  different 
parts  of  the  cerebellum  and  with  parts  above. 


Cb 


FIG.  132.  —  Human  brain  viewed  from  below.     C.  Cerebrum.      Cb.  Cere- 
bellum.    At,  Midbrain.     P.  Pons.     B,  Bulb.     I-XII.  Cranial  nerves. 


The  Bulb,  or  medulla  oblongata,  is,  properly  speaking, 
an  enlargement  of  the  spinal  cord  within  the  cranial  cav- 
ity. It  is  somewhat  triangular  in  shape,  and  lies  im- 
mediately below  the  cerebellum.  It  contains  important 
clusters  of  cell-bodies,  as  well  as  the  nerve  fibers  that  pas« 
from  the  spinal  cord  to  the  brain. 


292 


COORDINATION    AND    SENSATION 


SG. 


S<7. 


The  Spinal  Cord.  —  This  division  of 
the  central  nervous  system  is  about 
seventeen  inches  in  length  and  two 
thirds  of  an  inch  in  diameter.  It  does 
not  extend  the  entire  length  of  the 
spinal  cavity,  as  might  be  supposed,  but 
terminates  at  the  lower  margin  of  the 
first  lumbar  vertebra.1  It  connects  at 
the  upper  end  with  the  bulb,  and  termi- 
nates at  the  lower  extremity  in  a  number 
of  large  nerve  roots,  which  are  con- 
tinuous with  the  nerves  of  the  hips  and 
legs  (Fig.  133).  Two  deep  fissures,  one 
in  front  and  the  other  at  the  back,  ex- 
tend, the  entire  length  of  the  cord,  and 
separate  it  into  two  similar  divisions. 
These  are  connected,  however,  along 
their  entire  length  by  a  central  band 
consisting  of  both  gray  and  white 
matter. 

The  arrangement  of  the  neurons  of 
the  spinal  cord  is  just  the  reverse  of 

*In  very  early  life  the  spinal  cord  entirely  fills  the 
spinal  cavity,  but  as  the  body  develops  the  cord  grows 
less  rapidly  than  the  spinal  column,  and,  as  a  conse- 
quence, separates  at  the  lower  end  from  the  inclosing 
bony  column. 


FIG.  133. 


FIG.  133.  —  Spinal  cord,  showing  on  one  side 
the  nerves  and  ganglia  with  which  it  is  closely 
related  in  function.  A.  Bulb.  B.  Cervical  enlarge- 
ment. C.  Lumbar  enlargement.  D.  Termination 
of  cord.  E.  Nerve  roots  that  occupy  the  spinal 
cavity  below  the  cord.  P.  Pons.  D,  G.  Dorsal 
root  ganglia.  S.G.  Sympathetic  ganglia.  N.  Nerve 
trunks  to  upper  and  lower  extremities. 


STRUCTURE  OF  THE  NERVOUS   SYSTEM          293 

that  in  the  cerebrum  —  the  center  being  occupied  by  a 
double  column  of  cell-bodies,  which  give  it  a  grayish 
appearance,  while  the  fibers  occupy  the  outer  portion  of 
the  cord,  giving  it  a  whitish  appearance. 

The  spinal  cord  is  not  uniform  in  thickness,  but  tapers  slightly, 
though  not  uniformly,  from  the  upper  toward  the  lower  end.  At  the 
places  where  the  nerves  from  the  arms  and  legs  enter  the  cord  two  en- 
largements are  to  be  found,  the  upper  being  called  the  cervical  and  the 
lower  the  lumbar  enlargement.  These,  on  account  of  the  difference  in 
length  between  the  cord  and  the  spinal  cavity,  are  above  —  the  lower 
one  considerably  above  —  the  places  where  the  limbs  which  they  supply 
join  the  trunk  (Fig.  133). 

Arrangement  of  the  Neurons  of  the  Brain  and  Cord.  —  The  cell- 
bodies  in  the  brain  and  spinal  cord  are  collected  into  groups,  and  their 
fibers  extend  from  these  groups  to  places  that  may  be  near  or  remote. 
Guided  by  the  white  and  gray  colors  of  the  nervous  tissue,  and 
also  by  the  structures  revealed  by  the  microscope,  physiologists  have 
made  out  three  general  schemes  in  the  grouping  of  cell-bodies,  as 
follows : 

1 .  That  of  srtrface  distribution,  the  cell-bodies  forming  a  thin  but 
continuous  layer  over  a  given  surface.     This  is  the  plan  in  the  cere- 
brum and  cerebellum,  and  here  are  found  devices  for  increasing  the 
surface :    the  cerebrum  having  convolutions,  the  cerebellum  transverse 
ridges. 

2.  That  of  collections  of  cell-bodies  into    rounded  masses.     Such 
masses  are  found  in  the  bulb,  the  pons,  the  midbrain,  and  the  base  of 
the  cerebrum. 

3.  That  of  arrangement  in  a  continuous  column.     This  is  the  plan 
in  the  spinal  cord.     It  matters  not  at  what  place  the  spinal  cord  be  cut, 
a  central  area  of  gray  matter,  resembling  in  form  the  capital  letter  H,  is 
always  found. 

The  fibers  connecting  with  the  cell-bodies  in  the  brain  and  spinal 
cord  are  gathered  into  bundles  or  tracts,  and  these  pass  through  differ- 
ent parts  somewhat  as  follows  : 

I.  In  the  cerebrum  they  extend  in  three  general  directions,  forming 
three  classes  of  fibers.  The  first  connect  different  localities  in  the 
same  hemisphere,  and  are  known  as  association  fibers  (A,  Fig.  134). 
The  second  make  connection  between  the  two  hemispheres,  and  form 


294 


COORDINATION    AND    SENSATION 


the  corpus  callosum.  These  are  known  as  commissural  fibers  (C,  Fig. 
134).  The  third  connect  the  cerebrum  with  the  parts  of  the  nervous 
system  below,  and  are  called  projection  fibers  (/>,  Fig.  134). 

2.  In  the  cerebellum  both  association  and  commissural  fibers  are 
found.  Bands  of  fibers,  passing  upward  toward  the  cerebrum  and 
downward  toward  the  cord,  connect  this  part  of  the  brain  with  other 
parts  of  the  nervous  system. 


FIG.  r34.  —  Semi-diagrammatic  representation  of  a  section  through 
the  right  cerebral  hemisphere,  showing  fiber  tracts.  A.  Association  fibers. 
C.  Commissural  fibers.  P.  Projection  fibers.  The  cell-bodies  with  which  the 
fiber  bundles  connect  are  in  the  surface  layer  or  cortex. 


3.  In  the  midbrain,  bulb,  and  spinal  cord  fibers  are  found  :  first,  that 
connect  these  parts  with  the  cerebrum  J  and  cerebellum  above  ;  second, 

1  Fibers  passing  between  the  spinal  cord  and  the  cerebrum  cross  to  opposite 
sides — most  of  them  at  the  bulb,  but  many  within  the  cord  —  so  that  the  right 
side  of  the  cerebrum  is  connected  with  the  left  side  of  the  body,  and  vice  versa. 
This  accounts  for  the  observed  fact  that  disease  or  accidental  injury  of  one 
side  of  the  cerebrum  causes  loss  of  motion  or  of  feeling  in  the  opposite  side  of 
the  body. 


STRUCTURE   OF   THE   NERVOUS    SYSTEM          295 

that  pass  into  and  become  a  part  of  the  nerves  of  the  body ;  and  third, 
that  connect  the  opposite  sides  of  these  parts  together. 

The  Peripheral  Division. — The  peripheral  division  of 
the  nervous  system  includes  all  the  nervous  structures 
found  outside  of  the  brain  and  spinal  cord.  These  con- 
sist of  the  cranial,  spinal,  and  sympathetic  nerves,  and  of 
various  small  ganglia,  all  of  which  are  closely  connected 
with  the  central  system.  » 

Spinal  Nerves  and  Dorsal- root  Ganglia. — ^The  spinal 
nerves  comprise  a  group  of  thirty-one  pairs,  which  connect 
the  spinal  cord  with  different  parts  of  the  trunk,  with  the 
upper,  and  with  the  lower  extremities.  Each  nerve  joins 
the  cord  by  two  roots,  these  being  named  from  their  posi- 
tions the  ventral,  or  anterior,  root  and  the  dorsal,  or  pos- 
terior, root.  The  two  roots  blend  together  within  the 
spinal  cavity  to  form  a  single  nerve  trunk,  which  passes 
out  between  the  vertebrae.  On  the  dorsal  root  of  each 
spinal  nerve  is  a  small  ganglion  which  is  named,  from  its 
position,  the  dorsal-root  ganglion.  (Consult  Figs.  133  and 
135,  and  also  Fig.  125.) 

Double  Nature  of  Spinal  Nerves. — Charles  Bell,  in  1811, 
made  the  remarkable  discovery  that  each  spinal  nerve  is 
double  in  function.  He  found  the  portion  connecting 
with  the  cord  by  the  dorsal  root  to  be  concerned  in  the 
production  of  feeling  and  the  portion  connecting  by  the 
ventral  root  to  be  concerned  in  the  production  of  motion. 
In  keeping  with  these  functions,  the  two  divisions  of 
the  nerve  are  made  up  of  different  kinds  of  fibers,  as 
follows : 

1.  The  dorsal-root  divisions,  of  the  fibers  of  di-axonic 
neurons,    the   cell-bodies   of   which   form    the   dorsal-root 
ganglia  (Fig.  135). 

2.  The  ventral-root  divisions,  of  the  fibers  of  mon-axonic 


296 


COORDINATION   AND    SENSATION 


Spinal 
nerve 


neurons,  the  cell-bodies  of  which  are  in  the  gray  matter  ot 

the  cord. 

The  first  convey  impulses  to  the  cord   and    are  called 

afferent  neurons  ; 1  the  second  convey  impulses  from  the 

cord  and  are  known  as  efferent  neurons.  Thus,  by  form- 
ing a  part  of  the 
nerve  pathways 

.  between  the  skin 

and  the  brain, 
the  dorsal  divi- 
sions of  these 
nerves  aid  in  the 
production  of 
FIG.  135.  —  Connection  of  spinal  nerves  with  feeling'  and  by 

the  cord.     On  the  right  is  shown  a  nerve  pathway  ,    , . 

i  •  i       A  j-  •  •       r  nT-      n.    completing  path- 

from  the  skin  to  the  muscle.     A  division  of  this  path- 
way reaches  the  brain.  wa.VS  to  the  mus- 

cles,  the  ventral 

divisions  aid  in  the  production  of  motion  (Figs.  129,  135, 
and  141). 

The  Cranial  Nerves.  —  From  the  under  front  surface  of 
the  brain,  twelve  pairs  of  nerves  emerge  and  pass  to  the 
head,  neck,  and  upper  portions  of  the  trunk.  These,  the 
cranial  nerves,  have  names  suggestive  of  their  function  or 
distribution  and,  in  addition,  are  given  numbers  which  indi- 
cate the  order  in  which  they  leave  the  brain  (Fig.  136). 
Unlike  the  spinal  nerves,  the  cranial  nerves  present  great 
variety  among  themselves,  scarcely  any  two  of  them  being 
alike  in  function  or  in  their  connection  with  different  parts 
of  the  body.  Several  of  them  have  to  do  with  the  special 
senses,  and  are  for  this  reason  very  important.  They 

1  In  general,  afferent  neurons  or  fibers  are  those  that  convey  impulses  toward 
the  central  nervous  system  (brain  and  cord),  while  efferent  neurons  or  fibers  are 
those  that  convey  impulses  from  the  central  system. 


STRUCTURE   OF   THE   NERVOUS    SYSTEM          297 

connect   the   brain  with  the  different    parts  of  the  head, 
neck,  and  trunk,  as  follows : 

i.  The  first  pair  (olfactory  nerves;  nerves  of  smell; 
afferent)  connect  with  the  mucous  membrane  of  the 
nostrils  (Fig.  136). 


-Sp.  Cord 

-  1st  Sp.  Nerve 

-  2d  Sp.  Nerve 


FIG.  136.  —  Diagram  suggesting  the  distribution  and  functions  of  the 
cranial  nerves  (Colton).     See  also  Fig.  132. 

2.  The    second   pair  (optic   nerves  ;    nerves   of   sight ; 
afferent)  connect  with  the  retina  of  the  eyes. 

3.  The    third,  fourth,   and   sixth    pairs  (mot ores   oculi ; 
cdntrol  muscles  of  the  eyes ;   efferent)  connect  with  the 
internal  and  external  muscles  of  the  eyeballs  (Fig.  136). 

4.  The  fifth  pair  (trigeminal  nerves;  nerves  of  feeling 


298  COORDINATION  AND   SENSATION 

to  the  face,  of  taste  to  the  front  of  the  tongue,  and  of  con- 
trol of  muscles  of  mastication ;  afferent  and  efferent)  con- 
nect with  the  skin  of  the  face,  the  mucous  membrane  of 
the  mouth,  the  teeth,  and  the  muscles  of  mastication. 

5.  The   seventh   pair  {facial  nerves;    control  muscles 
that   give  the   facial  expressions ;    efferent)  connect  with 
the  muscles  just  beneath  the  skin  of  the  face. 

6.  The  eighth  pair  (auditory  nerves ;  nerves  of  hearing; 
afferent)  connect  with  the  internal  ear. 

7.  The   ninth    pair   {glossopharyngeal   nerves;    nerves 
of  taste  to  back  of  tongue  and  of  muscular  control  of 
pharynx;    afferent  and   efferent)  connect  with  the   back 
surface  of  the  tongue  and  with  the  muscles  of  the  pharynx. 

8.  The   tenth    pair  (vagus,  or   pneumogastric,   nerves ; 
nerves  of  feeling  and  of  muscular  control ;    afferent  and 
efferent)  connect  with  the  heart,  larynx,  lungs,  and  stom- 
ach.    They  have   the  widest  distribution   of   any  of   the 
cranial  nerves. 

9.  The  eleventh  pair  (spinal  accessory  nerves ;  control 
muscles  of  neck;    efferent)  connect  with  the  muscles  of 
the  neck. 

•  10.  The  twelfth  pair  (Jiypoglossal  nerves;  control  mus- 
cles of  the  tongue ;  efferent)  connect  with  the  muscles  of 
the  tongue. 

Sympathetic  Ganglia  and  Nerves. — The  sympathetic 
ganglia  are  found  in  different  parts  of  the  body,  and 
vary  in  size  from  those  which  are  half  an  inch  in  diameter 
to  those  that  are  smaller  than  the  heads  of  pins.  The 
largest  and  most  important  ones  are  found  in  two  chains 
which  lie  in  front,  and  a  little  to  either  side,  of  the  spinal 
column,  and  extend  from  the  neck  to  the  region  of  the 
pelvis  (Figs.  125  and  133).  The  number  of  ganglia  in  each 
of  these  chains  is  about  twenty-four.  They  are  connected 


STRUCTURE   OF   THE   NERVOUS   SYSTEM 


299 


on  either  side  by  the  right  and  left  sympathetic  nerves  which 
extend  vertically  from  ganglion  to  ganglion.  In  addition 
to  the  ganglia  forming  these  chains,  important  ones  are 
found  in  the  head  (outside  of  the  cranial  cavity)  and  in  the 
plexuses  of  the  thorax  and  the  abdomen. 

The  sympathetic  ganglia  receive  nerves  from  the  cen- 
tral division  of  the  nervous  system,  but  connect  with 
glands,  blood  vessels,  and  the  intestinal  walls  through 
fibers  from  their  own  cell-bodies.  Some  of  these  latter 
fibers  join  the  spinal  nerves,  and  some  blend  with  each 
other  to  form  small  sympathetic  nerves. 

Protection  of  Brain  and  Spinal  Cord.  —  On  account  of 
their  delicate  structure,  the  brain  and  spinal  cord  require 
the  most  complete  protection.  In  the  first  place,  they  are 
surrounded  by  the  bones  of  the  head  and  spinal  column ; 
these  not  only  shield  them  from  the  direct  effects  of 
physical  force,  but  by  their  peculiar  construction  prevent, 
to  a  large  degree,  the  passage  of  jars  and  shocks  to  the 
parts  within.  In  the  second  place,  they  are  surrounded  by 
three  separate  membranes,  as  follows : 

1.  The  dura,  or  dura  mater,  a  thick,  dense,  and  tough 
membrane  which  lines  the  bony  cavities  and  forms  sup- 
porting partitions. 

2.  The  pia,  or  pia  mater,  a  thin,  delicate  membrane, 
containing  numerous  blood  vessels,  that  covers  the  surface 
of  the  brain  and  cord. 

3.  The  arachnoid,  a  membrane  of  loose  texture,  that 
lies  between  the  dura  and  the  pia. 

Finally,  within  the  spaces  of  the  arachnoid  is  a  lymph- 
like  liquid  which  completely  envelops  the  brain  and  the 
cord,  and  which,  by  serving  as  a  watery  cushion,  protects 
them  from  jars  and  shocks.  Thus  the  brain  and  cord  are 
directly  shielded  by  bones,  by  membranes,  and  by  the 


300  COORDINATION   AND    SENSATION 

liquid  which  surrounds  them.  They  are  also  protected 
from  jars  resulting  from  the  movements  of  the  body  by 
the  general  elasticity  of  the  skeleton. 

Summary. — The  nervous  system  establishes  connections 
between  all  parts  of  the  body,  and  provides  a  stimulus  by 
means  of  which  they  are  controlled.  It  is  made  up  of  a 
special  form  of  cells,  called  neurons.  The  neurons  form 
the  different  divisions  of  the  nervous  system,  and  also  serve 
as  the  active  agents  in  carrying  on  its  work.  Through  a 
side-by-side  method  of  joining  they  form  the  nerves,  gan- 
glia, spinal  cord,  and  brain;  and  by  a  method  of  end-to-end 
joining  they  connect  places  remote  from  each  other,  and 
provide  for  nervous  movements  through  the  body.  The 
nervous  system  may  in  some  respects  be  compared  to  a 
complicated  system  of  telephony,  in  which  the  chains  of 
neurons  correspond  to  the  wires,  and  the  brain  and  spinal 
cord  to  the  central  station. 

Exercises.  —  i .  Give  the  meaning  of  the  term  "  coordination."  Sup- 
ply illustrations. 

2.  What  two  general  conditions  are  supplied  in  the  body  by  the 
nervous  system? 

3.  Compare  the  skeleton  outline  of  the  nervous  system  with  the 
bony  skeleton. 

4.  Sketch  outlines  of  mon-axonic  and  di-axonic  neurons. 

5.  Give  two  differences  between  the  neurons  and  the  other  cells  of 
the  body. 

6.  Describe  the  two  general  methods  of  connecting  neurons  in  the 
Dody.     What  purpose  is  accomplished  by  each  method  ? 

7.  Name  and  locate  the  principal  divisions  of  the  nervous  system. 

8.  Draw  an  outline  of  the  brain  (side  view),  locating  each  of  its 
principal  divisions. 

9.  If  a  pencil  were  placed  over  the  ear,  what  portions  of  the  brain 
would  be  above  it  and  what  below? 

10.  Describe  briefly  the  cerebrum,  the  cerebellum,  the  midbrain, 
the  pons,  and  the  bulb. 


STRUCTURE   OF   THE   NERVOUS    SYSTEM 


301 


11.  Locate  and  describe  the  cortex.     State  purpose  of  the  convolu- 
tions, 

12.  State  the  general  differences  between  the  cranial  and  the  spinal 
nerves. 

.     13.    Locate  and  give  the  number  of  the  dorsal-root  ganglia.     Locate 
and  give  the  approximate  number  of  the  sympathetic  ganglia. 

14.  Show  how  the  two  portions  of  the  spinal  nerves  are  formed  — 
the  one  from  the  mon-axonic  and  the  other  from  the  di-axonic  neurons. 

15.  Enumerate  the  different  agencies  through  which  the  brain  and 
spinal  cord  are  protected. 

1 6.  What  cranial  nerves  contain  afferent  fibers?     What  ones  contain 
efferent  fibers?     What  ones  contain  both  afferent  and  efferent  fibers? 

17.  In  what  respects  is  the  nervous  system  similar  to  a  system  of 
telephony?     In  what  respects  is  it  different? 


PRACTICAL   WORK 

Examine  a  model  of  the  brain,  identifying  the  different  divisions  and 
noting  the  position  and  relative  size  of  the  different  parts  (Fig.  137). 
Observe  the  convolutions  of  the  cerebrum  and  compare  these  with  the 
parallel  ridges  of  the  cerebellum.  If  the  model  is  dissectible,  study  the 
arrangement  of  the  cell-bodies  (gray  matter)  and  the  distribution  of  the 
fiber  bundles  (white 
matter).  Note  the 
connection  of  the 
cranial  nerves  with 
the  under  side. 

A  prepared  nervous 
system  of  a  frog  (such 
as  may  be  obtained 
from  supply  houses) 
should  also  be  ex- 
amined. Observe  the 


FIG.  137.  —  Model  for  demonstrating  the  brain 
(dissectible). 


appearance  and  general  distribution  of  the  nerves  and  their  connection 
with  the  brain  and  spinal  cord.  If  such  a  preparation  is  not  at  hand, 
some  small  animal  may  be  dissected  to  show  the  main  divisions  of 
the  nervous  system,  as  follows : 

Dissection  of  the  Nervous  System  (by  the  teacher).  — For  this  pur- 
pose a  half-grown  cat  is  generally  the  .best  available  material.     This 


302  COORDINATION    AND    SENSATION 

should  be  killed  with  chloroform  and  secured  to  a  board  as  in  the  dis- 
section of  the  abdomen  (page  169).  Open  the  abdominal  cavity  and 
remove  the  contents,  tying  the  alimentary  canal  where  it  is  cut,  and 
washing  out  any  blood  which  may  escape.  Dissect  for  the  nervous 
system  in  the  following  order : 

1.  Cut  away  the  front  of  the  chest,  exposing  the  heart  and  lungs. 
Find  on  each  side  of  the  heart  a  nerve  which  passes  by  the  side  of  the 
pericardium  to   the  diaphragm.      These   nerves   assist   in  controlling 
respiration  and  are  called  the  phrenic  nerves.     Find  other  nerves  going 
to  different  parts  of  the  thorax. 

2.  Remove   the   heart   and   lungs.     Find  in   the  back  part  of  the 
thoracic  cavity,  on  each  side  of  the  spinal  column,  a  number  of  small 
"  knots  "  of  nervous  matter  joined  together  by  a  single  nerve.     These 
are  sympathetic  ganglia.     Where  the  neck  joins  the  thorax,  find  two 
sympathetic  ganglia  much  larger  than  the  others. 

3.  Cut  away  the  skin  from  the  shoulder  and  upper  side  of  the  fore 
leg.     By  separating  the  muscles  and  connective  tissue  where  the  leg 
joins  the  thorax,  find  several  nerves  of  considerable  size.     These  con- 
nect with  each  other,  forming  a  network  called   the  brachial  plexus. 
From  here  nerves  pass  to  the  thorax  and  to  the  fore  leg. 

4.  From  the  brachial   plexus   trace  out   the  nerves  which   pass   to 
different  parts  of  the  fore  leg.     In  doing  this  separate  the  muscles  with 
the  fingers  and  use  the  knife  only  where  it  is  necessary  to  expose  the 
nerves.     Note  that  some  of  the  branches  pass  into  the  muscles,  while 
others  connect  with  the  skin. 

5.  Remove  the  skin  from  the  upper  portion  of  one  of  the  hind  legs 
and  separate  the  muscles  carefully  until  a  large  nerve  is  found.     This 
is  one  of  the  divisions  of  the  sciatic  nerve.     Carefully  trace  it  to  the 
spinal  cord,  cutting  away  the  -bone  where  necessary,  and  find  the  con- 
nections of  its  branches  with  the  cord.     Then  trace  it  toward  the  foot, 
discovering  its  branches  to  different  muscles  and  to  the  skin. 

6.  Unjoint  the  neck  and  remove  the  head.     Examine  the  spinal  cord 
where  exposed.     Cut  away  the  bone  sufficiently  to  show  the  connection 
between  the  cord  and  one  of  the  spinal  nerves.     On  the  dorsal  root 
of  one  of  the  nerves  find  a  small  ganglion.     What  is  it  called? 

7.  Fasten  the  head  to  a  small  board  and  remove  the  scalp.     Saw 
through  the  skull  bones  in  several  directions.     Pry  off  the  small  pieces 
of  bones,  exposing  the  upper  surface  of  the  brain.     Study  its  mem- 
branes, convolutions,  and  divisions. 


STRUCTURE   OF   THE  NERVOUS   SYSTEM          303 

8.  With  a  pair  of  bone  forceps,  or  nippers,  break  away  the  skull 
until  the  entire  brain'  can  be  removed  from  the  cavity.     Examine  the 
different  divisions,  noting  the  relative  position  and  size  of  the  parts. 

9.  With  a  sharp  knife  cut  sections  through  the  different  parts,  show- 
ing the  positions  of  the  "  gray  matter  "  and  of  the  "  white  matter." 

NOTE.  —  If  the  entire  class  is  to  examine  one  specimen,  it  is  gen- 
erally better  to  have  the  dissecting  done  beforehand  and  the  parts  sep- 
arated and  tacked  to  small  boards.  This  will  permit  of  individual 
examination.  Sketches  of  the  sciatic  nerve,  brachial  plexus,  and  of 
sections  through  the  brain  and  spinal  cord  should  be  made. 

Location  of  Nerves  in  the  Body.  —  Several  of  the  nerves  of  the  body 
lie  sufficiently  near  the  surface  to  be  located  by  pressure  and  are  easily 
recognized  as  sensitive  cords.  Slight  pressure  from  the  fingers  reveals 
the  presence  of  nerves  in  the  grooves  of  the  elbow  (the  crazy  bone), 
between  the  muscles  on  the  inner  side  of  the  arm  near  the  shoulder, 
and  in  the  hollow  part  of  the  leg  back  of  the  knee.  These  are  all  large 
nerves.  Small  nerves  may  be  located  in  the  same  manner  in  the  face 
and  neck. 


CHAPTER   XVIII 
PHYSIOLOGY  OF  THE  NERVOUS  SYSTEM 

IN  the  preceding  chapter  was  pointed  out  the  method 
by  which  the  different  parts  of  the  body  are  brought  into 
communication  by  the  neurons  or  nerve  cells.  We  are 
now  to  study  the  means  whereby  the  neurons  are  made 
to  control  and  coordinate  the  different  parts  of  the  body 
and  bring  about  the  necessary  adjustment  of  the  body  to 
its  surroundings.  This  work  of  the  neurons  naturally  has 
some  relation  to  their  properties. 

Properties  of  Neurons.  —  The  work  of  the  neurons  seems 
to  depend  mainly  upon  two  properties  —  the  property  of 
irritability  and  the  property  of  conductivity.  Irritability 
was  explained,  in  the  study  of  the  muscles  (page  243),  as 
the  ability  to  respond  to  a  stimulus.  It  has  the  same 
meaning  here.  The  neurons,  however,  respond  more 
readily  to  stimuli  than  do  the  muscles  and  are  therefore 
more  irritable.  Moreover,  they  are  stimulated  by  all  the 
forces  that  induce  muscular  contraction  and  by  many 
others  besides.  They  are  by  far  the  most  irritable  por- 
tions of  the  body. 

Conductivity  is  the  property  which  enables  the  effect  of 
a  stimulus  to  be  transferred  from  one  part  of  a  neuron 
to  another.  On  account  of  this  property,  an  excitation, 
or  disturbance,  in  any  part  of  a  neuron  is  conducted  or 
carried  to  all  the  other  parts.  Thus  a  disturbance  at  the 
distant  ends  of  the  dendrites  causes  a  movement  toward 
the  cell-body  and,  reaching  the  cell-body,  the  disturbance  is 

3°4 


PHYSIOLOGY   OF   THE   NERVOUS   SYSTEM         305 

passed  through  it  into  the  axon.     This  movement  through 
the  neuron  is  called  the  nervous  impulse. 

Purpose  of  the  Impulse.  — :  Though  the  nature  of  the  nerv 
ous  impulse  is  not  understood,1  its  purpose  is  quite  appar- 
ent. It  is  the  means  employed  by  the  nervous  system 
for  controlling  and  coordinating  the  different  parts  of  the 
body.  The  arrangement  of  the  neurons  enables  impulses 
to  be  started  in  certain  parts  of  the  nervous  system,  and 
the  property  of  conductivity  causes  them  to  be  passed  as 
stimuli  to  other  parts.  This  enables  excitation  at  one  place 
to  bring  about  action  at  another  place. 

Acting  as  stimuli,  the  impulses  seem  able  to  produce 
two  distinct  effects :  first,  to  throw  resting  organs  into 
action  and  to  increase  the  activity  of  organs  already  at 
work ;  and  second,  to  diminish  the  rate,  or  check  entirely, 
the  activity  of  organs.  Impulses  producing  the  first  effect 
are  called  excitant  impulses ;  those  producing  the  second 
effect,  inhibitory  impulses. 

Functions  of  the  Parts  of  Neurons.  —  The  cell-body  serves 
as  a  nutritive  center  from  which  the  other  parts  derive 
nourishment.  Proof  of  this  is  found  in  the  fact  that  when 
any  part  of  the  neuron  is  separated  from  the  cell-body,  it 
dies,  while  the  cell-body  and  the  parts  attached  to  the  cell- 


l  At  different  times  the  nervous  impulse  has  been  regarded  as  a  current  of 
electricity;  as  a  progressive  chemical  change,  likened  to  that  in  a  burning  fuse; 
as  a  mechanical  vibration,  such  as  may  be  passed  over  a  stretched  rope;  and  as 
a  molecular  disturbance  accompanied  by  an  electrical  discharge.  The  velocity  of 
the  nervous  impulse,  which  is  only  about  one  hundred  feet  per  second,  proves  that 
it  is  not  a  current  of  electricity.  It  takes  place  with  little  or  no  exhaustion  of  the 
cell  protoplasm  and  consequently  is  not  due  to  chemical  action.  And  the  loose, 
relaxed  condition  of  the  nerves  prevents  their  transmission  of  physical  vibrations, 
like  those  on  a  stretched  rope.  The  view  that  the  impulse  is  a  progressive  molecu- 
lar disturbance,  accompanied  by  an  electrical  discharge,  has  much  evidence  in  its 
favor,  but  it  has  only  recently  been  proposed  and  is  likely  to  be  modified  upon 
fuller  investigation. 


306  COORDINATION    AND    SENSATION 

body  may  continue  to  live.  In  addition  to  this  the  cell- 
body  probably  reenforces  the  nervous  impulse. 

The  dendrites  serve  two  purposes :  first,  they  extend 
the  surface  of  the  cell-body,  thereby  enabling  it  to  absorb 
a  greater  amount  of  nourishment  from  the  surrounding 
lymph ;  second,  they  act  as  receivers  of  stimuli  from 
other  neurons.  The  same  impulse  does  not  pass  from  one 
neuron  to  another.  An  impulse  in  one  neuron,  however, 
is  able  to  excite  the  neuron  with  which  it  makes  an  end- 
to-end  connection,  so  that  a  series  of  impulses  is  produced 
along  a  given  nerve  path  (Fig.  129). 

The  special  function  of  the  axon  is  to  transmit  the  impulse. 
By  its  length,  structure,  and  property  of  conductivity  it  is 
especially  adapted  to  this  purpose.  The  axis  cylinder, 
however,  is  the  only  part  of  the  axon  concerned  in  the 
transmission.  The  primitive  sheath  and  the  medullary 
layer  protect  the  axis  cylinder,  and,  according  to  some  au- 
thorities, serve  to  insulate  it.  The  medullary  sheath  may 
also  aid  in  the  nourishment  of  the  axis  cylinder. 

Nerve  Stimuli.  —  While  the  properties  of  irritability  and 
conductivity  supply  a  necessary  cause  for  the  production 
and  transmission  of  nervous  impulses,  these  alone  are  not 
sufficient  to  account  for  their  origin.  An  additional  cause 
is  necessary  —  a  force  not  found  in  the  nerve  protoplasm, 
but  one  which,  by  its  action  on  the  protoplasm,  makes  it 
produce  the  impulse.  In  this  respect,  the  neuron  does 
not  differ  essentially  from  the  cell  of  a  muscle.  Just  as 
the  muscle  cell  requires  a  stimulus  to  make  it  contract,  so 
does  the  neuron  require  a  stimulus  to  start  the  impulse. 
Hence,  in  accounting  for  the  activities  of  the  body,  it  is  not 
sufficient  to  say  they  are  caused  by  nervous  impulses.  We 
must  also  investigate  the  nerve  stimuli  —  the  means  through 
which  the  nervous  impulses  are  started.  Most  of  these 


PHYSIOLOGY    OF    THE   NERVOUS    SYSTEM          307 

are  found  outside  of  the  body  and  are  known  as  external 
stimuli. 

Action  of  External  Stimuli.  —  In  the  arrangement  of  the 
nervous  system  the  most  favorable  conditions  are  provided 
for  the  reception  of  external  stimuli.  Not  only  do  vast 
numbers  of  neurons  terminate  at  the  surface  of  the  body,1 
but  they  connect  there  with  delicate  structures,  called  sense 
organs.  The  purpose  of  the  sense  organs  is  to  sensitize 
(make  sensitive)  the  terminations  of  the  neurons.  This 
they  do  by  supplying  special  structures  through  which  the 
stimuli  can  act  to  the  best  advantage  upon  the  nerve  end- 
ings. Moreover,  there  are  different  kinds  of  sense  organs, 
and  these  cause  the  neurons  to  be  sensitive  to  different 
kinds  of  stimuli.  Acting  through  the  sense  organs  adapted 
for  receiving  them,  light,  sound,  heat,  cold,  and  odors  all 
act  as  stimuli  for  starting  impulses.  Indeed,  the  arrange- 
ment is  so  complete  that  the  nervous  system  is  subjected 
to  the  action  of  external  stimuli  in  some  form  practically 
all  the  time.  The  work  of  the  sense  organs  is  further  con- 
sidered in  Chapters  XX,  XXI,  and  XXII. 

How  External  Stimuli  act  on  Internal  Organs.  —  For 
stimulating  the  neurons  not  connected  with  the  body  sur- 
face we  are  dependent,  so  far  as  known,  upon  the  nervous 
impulses.  An  impulse  started  by  the  external  stimulus 
goes  only  so  far  as  its  neuron  extends.  But  it  serves  as  a 
stimulus  for  the  neuron  with  which  the  first  connects  and 
starts  an  impulse  in  this  connecting  neuron,  the  point  of 
stimulation  being  where  the  fiber  terminations  of  the  first 
neuron  make  connection  with  the  dendrites  of  the  second. 
This  impulse  in  turn  stimulates  the  next  neuron,  and  so  on, 
producing  a  series  of  impulses  along  a  given  nerve  path. 

i  The  surface  of  the  body  includes  the  linings  of  the  air  passages,  food  canal, 
and  certain  cavities,  as  well  as  the  external  covering  or  skin. 


308 


COORDINATION    AND    SENSATION 


In  this  way  the  effect  of  an  external  stimulus  may  reach 
and  bring  about  action  in  any  part  of  the  body.  This  is  in 
brief  the  general  plan  of  inducing  action  in  the  various 
organs  of  the  body.  This  plan,  however,  is  varied  according 
to  circumstances,  'and  at  least  three  well-defined  forms  of 
action  are  easily  made  out.  These  are  known  as  reflex 
action,  voluntary  action,  and  secondary  reflex  action. 

Reflex  Action.  —  When  some  sudden  or  strong  stimulus 
acts  upon  the  nerve  terminations  at  the  surface  of  the 
body,  an  immediate  response  is  frequently  observed  in 


MUSCLE 


SPINAL  CORD 
FIG.  138.  — Diagram  illustrating  reflex  action  of  an  external  organ. 

some  quick  movement.  The  jerking  away  of  the  hand 
on  accidentally  touching  a  hot  stove,  the  winking  of  the 
eyes  on  sudden  exposure  to  danger,  and  the  quick  move- 
ments from  slight  electrical  shocks  are  familiar  examples. 
The  explanation  of  reflex  action  is  that  external  stimuli 
start  impulses  in  neurons  terminating  at  the  surface  of  the 
body  and  these,  in  turn,  excite  impulses  in  neurons  which 
pass  from  the  spinal  cord  or. brain  to  the  muscles  (Fig. 
138).  Since  there  is  an  apparent  turning  back  of  the 
impulses  by  the  cord  or  brain,  the  resulting  movements 
are  termed  reflex?- 

Reflex  Action  and  the  Mind.  —  If  one  carefully  studies 
the  reflex  actions  of  his  own  body,  he  will  find  that  they 

1  Derived  from  the  Latin  re,  back,  &n&Jlectere,  to  turn  or  bend. 


PHYSIOLOGY   OF   THE   NERVOUS   SYSTEM         309 

occur  at  the  time,  or  even  a  little  before  the  time,  that  he 
realizes  what  has  happened.  If  a  feather  is  brought  in 
contact  with  the  more  sensitive  parts  of  the  face  of  a 
sleeping  person,  there  is  a  twitching  of  the  skin  and  some- 
times a  movement  of  the  hand  to  remove  the  offending 
substance.  Surgeons  operating  upon  patients  completely 
under  the  influence  of  chloroform,  and  therefore  com- 
pletely unconscious,  have  observed  strong  reflex  actions. 
These  and  other  similar  cases  indicate  clearly  that  reflex 
action  occurs  independently  of  the  mind  —  that  the  mind 
neither  causes  nor  controls  it.  If  a  further  proof  of  this 
fact  were  needed,  it  is  supplied  by  experiments  upon  cer- 
tain of  the  lower  animals,1  which  live  for  a  while  after  the 
removal  of  the  brain.  These  experiments  show  that  the 
nervous  impulses  that  produce  reflex  action  need  only  pass 
through  the  spinal  cord  and  do  not  reach  the  cerebrum,  the 
organ  of  the  mind. 

The  Reflex  Action  Pathway.  —  By  study  of  the  impulses 
that  produce  any  reflex  action,  a  rather  definite  pathway 
may  be  made  out,  having  the  following  divisions  : 

I .  From  the  surface  of  the  body  to  the  central  nervous  sys- 
tem (usually  the  spinal  cord).  This,  the  afferent  division,  is 
made  up  of  di-axonic  neurons,  and  these  have  (in  the  case  of 
the  spinal  nerves)  their  cell-bodies  in  the  dorsal  root  ganglia 
(page  295).  They  are  acted  upon  by  external  stimuli,  while 
their  impulses  in  turn  act  on  the  neurons  in  the  spinal  cord. 

l  A  frog  from  which  the  brain  has  been  removed  is  suspended  with  its  feet 
downward  and  free  to  move.  If  a  toe  is  pinched,  the  foot  is  drawn  away,  and 
if  dilute  acid,  or  a  strong  solution  of  salt,  is  placed  on  the  tender  skin,  the  feet  are 
moved  as  if  to  take  away  the  irritating  substance.  This  of  course  shows  that  reflex 
action  can  take  place  independently  of  the  brain. 

Now  if  the  spinal  cord  is  also  destroyed,  there  is  no  response  when  the  irritation 
of  the  skin  is  repeated.  The  animal  remains  perfectly  quiet,  because  the  destruc- 
tion of  the  cord  has  interrupted  the  reflex  action  pathway.  This  shows  that  some 
part  of  the  central  nervous  system  is  necessary  to  reflex  action. 


3io 


COORDINATION   AND   SENSATION 


2.  Through  the  central  system  (spinal  cord  or  base  of 
brain).     This,  the  intermediate  division,  may  be  composed 
of  mon-axonic  neurons,  or  it  may  consist  of  branches  from 
the  afferent  neurons.      In  the  case   of  separate  neurons, 
these    are    acted    upon    by   impulses    from    the    afferent 
neurons,  while  their  impulses  serve  in  turn  as  stimuli  to 
other  neurons  within  the  cord  (Fig.  129). 

3.  From  the  central  nervous  system  to  the  muscles.    This, 
the  efferent  division,  is  made  up  of  mon-axonic  neurons. 
Most  of  these  have  their  cell-bodies  in  the  gray  matter  of 
the  cord,  while  their  fibers  pass  into  the  spinal  nerves  by 
the  ventral  roots.1     They  may  be  stimulated  by  impulses 
either  from  the  intermediate  neurons,  or  from  branches  of 
the  afferent  neurons.     Their  impulses  reach  and  stimulate 
the  muscles. 

Reflex  Action  in  Digestion.  —  The  flowing  of  the  saliva,  when  food 
is  present  in  the  mouth,  is  an  example  of  reflex  action.     In  this  case, 

however,  the  organ 
excited  to  activity  is 
a  gland  instead  of  a 
muscle.  The  food 
starts  the  impulses, 
and  these,  acting 
through  the  bulb, 
reach  and  stimulate 
the  salivary  glands. 
In  a  similar  manner 
food  excites  the 
glands  that  empty 
their  fluids  into  the 

stomach  and  intestines,  and  stimulates  the  muscular  coats  of  these 
organs  to  do  their  part  in  the  digestive  process.  To  a  considerable 
extent,  neurons  having  their  cell-bodies  in  the  sympathetic  ganglia  are 
concerned  in  these  actions  (Fig.  139). 

Reflex  Action  in  the  Circulation  of  the  Blood.  —  On  sudden  exposure 

1  Review  description  of  the  spinal  nerves,  page  295. 


FIG.  139. —  Diagram  illustrating  reflex  action 
in  its  relation  to  the  food  canal.  The  nerve  path  in 
this  case  includes  sympathetic  neurons. 


PHYSIOLOGY   OF   THE   NERVOUS   SYSTEM         311 

to  cold,  the  small  arteries  going  to  the  skin  quickly  diminish  in  size, 
check  the  flow  of  blood  to  the  surface,  and  prevent  too  great  a  loss 
of  heat.  In  this  case,  impulses  starting  at  the  surface  of  the  body  are 
transmitted  to  the  bulb  and  then  through  the  efferent  neurons  to  the 
muscles  in  the  walls  of  the  arteries.  In  a  somewhat  similar  manner, 
heat  leads  to  a  relaxation  of  the  arterial  walls  and  an  increase  in  the 
blood  supply  to  the  skin.  Other  changes  in  the  blood  supply  to  differ- 
ent parts  of  the  body  are  also  of  the  nature  of  reflex  actions.  As  in  the 
work  of  digestion,  neurons  having  their  cell-bodies  in  the  sympathetic 
ganglia  aid  in  the  control  of  the  circulation. 

Purposes  of  Reflex  Action.  —  The  examples  of  reflex 
action  so  far  considered  illustrate  its  two  main  purposes  — 
(i)  protection,  and  (2)  a  means  of  controlling  important 
processes. 

The  pupil  has  but  to  study  carefully  the  reflex  actions 
of  his  own  body  for  a  period,  say  of  two  or  three  weeks, 
in  order  to  be  convinced  of  their  protective  value.  He 
will  observe  that  portions  of  his  body  have,  on  exposure  to 
danger,  been  moved  to  places  of  safety,  while  in  some 
instances,  like  falling,  his  entire  body  has  been  adjusted 
to  new  conditions.  He  will  also  find  that  reflex  action 
is  quicker,  and  for  that  reason  offers  in  some  cases  better 
protection,  than  movements  directed  by  the  mind.  In 
digestion  and  circulation  are  found  the  best  examples  of 
the  control  of  important  processes  through  reflex  action. 

Voluntary  Action.  —  It  is  observed  that  reflex  action,  in 
the  sense  that  it  has  so  far  been  considered,  is  not  the 
usual  mode  of  action  of  the  external  organs,  but  is,  instead, 
a  kind  of  emergency  action,  due  to  unusual  conditions  and 
excitation  by  strong  stimuli.  Voluntary  actions,  on  the  other 
hand,  represent  the  ordinary,  or  normal,  action  of  these 
organs.  They  comprise  the  movements  of  the  body  of 
which  we  are  conscious  and  which  are  controlled  by  the 
mind.  But  while  they  are  of  a  higher  order  than  reflex 


312 


COORDINATION    AND    SENSATION 


actions  and  are  under  intelligent  direction,  they  are  brought 

about  in  much  the  same  manner. 

Voluntary  Action  Pathways  differ  in  but  one  essential 

respect  from  those  of  reflex  action.     They  pass  through 

the  cerebrum,  the  organ  of  the  mind  (Fig.  140).     This  is 

necessary  in  order  that  the 
mind  may  control  the  action. 
From  all  portions  of  the 
body  surface,  afferent  path- 
ways may  be  traced  to  the 
cerebrum ;  and  from  the 
cerebrum  efferent  pathways 
extend  to  all  the  voluntary 
organs.  A  complex  system  of 
intermediate  neurons,  found 
mostly  in  the  brain,  join  the 
afferent  with  the  efferent 
pathways.  The  voluntary 
pathways  are  not  distinct 
from,  but  include,  reflex 
pathways,  a  fact  which  ex- 
plains why  the  same  external 


FIG.  140.  —  Diagram  of  a  voluntary 
action  pathway. 


stimulus  may  excite  both 
reflex  and  voluntary  action 
(Fig.  141). 

Choice  in  Voluntary  Action.  —  In  reflex  action  a  given 
stimulus,  acting  in  a  certain  way,  produces  each  time  the 
same  result.  This  is  not  the  case  with  voluntary  action, 
the  difference  being  due  to  the  mind.  In  these  actions  the 
external  stimulus  first  excites  the  mind,  and  the  resulting 
mental  processes  —  perhaps  as  memory  of  previous  experi- 
ences —  supply  a  variety  of  facts,  any  of  which  may  act  as 
stimuli  to  action.  Before  the  action  takes  place,  however, 


PHYSIOLOGY    OF   THE   NERVOUS    SYSTEM          313 


some  one  fact  must  be  singled  out  from  among  the  mental 

processes  excited.     This  fact  becomes  the  exciting  stimulus 

and    leads    to    action.       It 

follows,  therefore,  that  the 

action  which  finally  occurs 

is  not  necessarily  the  result 

of    an    immediate    external 

stimulus,  but   of    a  selected 

stimulus  —  one  which  is  the 

result  of  choice. 

Not  only  does  the  element 
of  choice  enter  into  the  selec- 
tion of  the  proper  stimulus, 
but  it  also  enters  into  the 
time,  nature,  and  intensity 
of  the  action.  For  these 
reasons  it  is  frequently  im- 
possible to  trace  voluntary 
actions  back  to  their  actual 
stimuli.  The  pupil  will  rec- 


M 


FIG.  141.  — Diagram  of  voluntary 


ognize  the  element  of  choice  action  pathways  including  reflex  path- 

...  .   .      ways, 

in  such  simple  acts  as  pick- 
ing up  some  object   from   the  street,  complying  with  a 
request,  and  purchasing  some  article  from  a  store. 

Reflex  and  Voluntary  Action  Compared.  —  Certain  like- 
nesses and  differences,  already  suggested  in  these  two 
forms  of  action,  may  now  be  more  fully  pointed  out. 
Reflex  and  voluntary  action  are  alike  in  that  the  primary 
cause  of  each  is  some  outside  force  or  condition  which  has 
impressed  itself  upon  the  nervous  system.  They  are  also 
alike  in  the  general  direction  taken  by  the  impulses  in 
producing  the  action.  The  impulses  are,  first,  from  the 
surface  of  the  body  to  the  central  nervous  system ;  second, 


314  COORDINATION   AND   SENSATION 

through  the  central  system ;  and  third,  from  the  central 
nervous  system  to  the  active  tissues  of  the  body. 

Their  chief  differences  are  to  be  found,  first,  in  the  path- 
ways followed  by  the  impulses,  which  are  through  the  cere- 
brum (the  organ  of  the  mind)  in  voluntary  action,  but  in 
reflex  action  are  only  through  the  spinal  cord  or  the  lower 
parts  of  the  brain ;  and  second,  in  the  fact  that  voluntary 
action  is  under  the  direction  of  the  mind,  while  reflex  action 
is  not.  It  would  seem,  therefore,  that  the  statement  some- 
times made  that  "voluntary  action  is  reflex  action  plus  the 
mind"  is  not  far  from  correct.  Mind,  however,  is  the  im- 
portant factor  in  this  kind  of  action. 

Secondary  Reflex  Action.  —  Everyday  experience  teaches 
that  any  voluntary  action  becomes  easier  by  repetition.  A 
given  act  performed  a  number  of  times  under  conscious 
direction  establishes  a  condition  in  the  nervous  system  that 
enables  it  to  occur  without  that  direction  and  very  much  as 
reflex  actions  occur.  Actions  of  this  kind  are  known  as 
secondary  reflex  actions,  or  as  acquired  reflexes.  Walking, 
writing,  and  numerous  other  movements  pertaining  to  the 
occupation  which  one  follows  are  examples  of  such  re- 
flexes. These  activities  are  at  first  entirely  voluntary,  but 
by  repetition  they  gradually  become  reflex,  requiring  only 
the  stimulus  to  start  them. 

The  advantages  to  the  body  of  its  acquired  reflexes  are 
quite  apparent.  The  mind  does  not  have  to  attend  to  the 
selection  and  direction  of  stimuli  and,  to  that  extent,  is  left 
free  for  other  work.  A  good  example  of  this  is  found 
in  writing,  where  the  mind  apparently  gives  no  heed  to 
the  movements  of  the  hand  and  is  only  concerned  in 
what  is  being  written.  The  student  will  easily  supply 
other  illustrations  of  the  advantages  of  secondary  reflex 
action. 


PHYSIOLOGY   OF   THE   NERVOUS   SYSTEM         315 

The  development  of  secondary  reflexes  probably  consists  in  the  es- 
tablishment of  fixed  pathways  for  impulses  through  the  nervous  system. 
Through  the  branching  of  the  nerve  fibers  many  pathways  are  open  to 
the  impulses.  But  in  repeating  the  same  kind  of  action  the  impulses 
are  guided  into  particular  paths,  or  channels.  In  time  these  paths  be- 
come so  well  established  that  the  impulses  flow  along  them  without 
conscious  direction  and  it  is  then  simply  necessary  that  some  stimulus 
starts  the  impulses.  By  following  the  established  pathways,  these  reach 
the  right  destination  and  produce  the  desired  result.  According  to  this 
view,  secondary  reflex  action  is  but  a  higher  phase  of  ordinary  reflex 
action  —  a  kind  of  reflex  action,  the  conditions  of  which  have  been 
established  by  the  mind  through  repetition.  (See  functions  of  the 
cerebellum,  page  317.) 

Habits.  —  People  are  observed  to  act  differently  when 
exposed  to  the  same  conditions,  or  when  acted  upon  by  the 
same  stimuli.  This  is  explained  by  saying  they  have  differ- 
ent habits.  By  habits  are  meant  certain  general  modes 
of  action  that  have  been  acquired  by  repetition.  Certain 
acts  repeated  again  and  again  have  established  conditions 
in  the  nervous  system  which  enable  definite  forms  of  action 
to  be  excited,  somewhat  after  the  manner  of  reflex  action. 
On  account  of  habits,  therefore,  the  actions  of  the  indi- 
vidual are  more  or  \QSS  predisposed.  What  he  will  do  under 
certain  conditions  may  be  foretold  from  his  habits.  Habits 
simply  represent  a  higher  order  of  secondary  reflexes  — 
those  more  closely  associated  with  the  mental  life  and 
character  than  are  the  lower  forms. 

Habits,  in  common  with  other  forms  of  secondary  reflex 
action,  serve  the  important  purpose  of  economising  the  nerv- 
ous energy.  However,  if  pernicious  habits  are  formed 
instead  of  those  that  are  useful,  they  are  detrimental  from 
both  a  moral  and  a  physical  standpoint.  Youth  is  recog- 
nized as  the  period  in  which  fundamental  habits  are  formed 
and  character  is  largely  determined.  Therefore  parents 


316  COORDINATION   AND    SENSATION 

and  teachers  do  wisely  when  they  insist  upon  the  formation 
of  right  habits  by  the  young. 

Functions  of  Divisions  of  the  Nervous  System.  —  The 
relationship  between  the  different  parts  of  the  nervous 
system  is  very  close  and  one  part  does  not  work  inde- 
pendently of  other  parts.  At  the  same  time  the  general 
work  of  the  nervous  system  requires  that  its  different 
divisions  serve  different  purposes : 

1.  The  peripheral  divisions  of  the  nervous  system  are 
concerned  in  the  transmission  of  impulses  between  the  sur- 
face of  the  body  and  the  central  system  and  between  the 
central  system  and  the  active  tissues.     The  nerves  are  the 
carriers  of  the  impulses.     The  ganglia  contain  the  cell- 
bodies  which  serve  as  nutritive  centers ;  and,  in  the  case  of 
the  sympathetic  ganglia,  these  cell-bodies  are  the  places 
where  the  fiber  terminations  of  one  neuron  connect  with, 
and  stimulate,  other  neurons. 

2.  The  gray  matter  in  the  spinal  cord,  bulb,  pons,  and 
midbrain  (through  the  cell-bodies,  fiber  terminations,  and 
short  neurons  which   they  contain)  completes   the   reflex 
action  pathways  between  the  surface  of  the  body  and  the 
voluntary  muscles,  and    also  between  the  surface  of   the 
body  and  the  organs  of  circulation  and  digestion. 

3.  The  white  matter  of  the  spinal  cord,  bulb,  pons,  and 
midbrain  (by  means  of  the  fibers  of  which  they  are  largely 
composed)  forms  connections  with,  and  passes  impulses  be- 
tween, the  various  parts  of  the  central  nervous  system. 

4.  The  bulb,  because  of  certain  special  reflex-action  path- 
ways completed  through  it,  is  the  portion  of  the  central 
nervous  system  concerned  in  the  control  of  respiration,  cir- 
culation, and  the  secretion  of  liquids. 

Work  of  the  Sympathetic  Ganglia  and  Nerves.  — The  neurons  which 
form  these  ganglia  aid  in  controlling  the  vital  processes,  especially  di- 


PHYSIOLOGY   OF   THE   NERVOUS    SYSTEM          317 

gestion  and  circulation.  These  neurons  are  controlled  for  the  most  part 
by  fibers  from  the  bulb  and  spinal  cord,  and  cannot  for  this  reason  be 
looked  upon  as  forming  an  independent  system.  Their  chief  purpose 
seems  to  be  that  of  spreading  the  influence  of  neurons  from  the  central 
system  over  a  wider  area  than  they  would  otherwise  reach.  For  ex- 
ample, a  single  neuron  passing  out  from  the  spinal  cord  may,  by  termi- 
nating in  a.  sympathetic  ganglion,  stimulate  a  large  number  of  neurons, 
each  of  which  will  in  turn  stimulate  the  cells  of  muscles  or  of  glands. 
Because  of  this  function,  the  sympathetic  neurons  are  sometimes  called 
distributing  neurons. 

Functions  of  the  Cerebellum.  —  Efforts  to  discover  some  special  func- 
tion of  the  cerebellum  have  been  in  the  main  unsuccessful.  Its  removal 
from  animals,  instead  of  producing  definite  results,  usually  interferes  in 
a  mild  way  with  a  number  of  activities.  The  most  noticeable  results 
are  a  general  weakness  of  the  muscles  and  an  inability  on  the  part  of 
the  animal  to  balance  itself.  This  and  other  facts,  including  the  man- 
ner of  its  connection  with  other  parts  of  the  nervous  system,  have  led 
to  the  belief  that  the  cerebellum  is  the  chief  organ  for  the  reflex  coordi- 
nation of  muscular  movements,  especially  those  having  to  do  with  the 
balancing  of  the  body.  In  this  connection  it  is  subordinate  to  and  un- 
der the  control  of  the  cerebrum.  Of  the  relations  which  the  cerebellum 
sustains  to  the  cerebrum  and  to  the  different  parts  of  the  body,  the  fol- 
lowing view  is  quite  generally  held  : 

In  the  development  of  secondary  reflexes,  as  already  described, 
conditions  are  established  in  the  cerebellum,  such  that  given  stimuli 
may  act  reflexhiely  through  it  and  produce  definite  results  in  the  way 
of  muscular  contraction.  After  the  establishment  of  these  conditions, 
afferent  impulses  from  the  eyes,  ears,  skin,  and  other  places,  under  the 
general  direction  of  the  cerebrum,  may  cause  such  actions  as  the  bal- 
ancing of  the  body,  walking,  etc.,  as  well  as  the  delicate  and  varied 
movements  of  the  hand.  This  view  of  its  functions  makes  of  the  cere- 
bellum the  great  center  of  secondary  reflex  action. 

Functions  of  the  Cerebrum.  —  While  the  work  of  the 
cerebrum  is  closely  related  to  that  of  the  general  nervous 
system,  it,  more  than  any  other  part,  exercises  functions 
peculiar  to  itself.  The  cerebrum  is  the  part  of  the  nervous 
system  upon  which  our  varied  experiences  leave  their  im- 
pressions and  through  which  these  impressions  are  made 


COORDINATION   AND   SENSATION 


Fissure  of  Rolando 


to  influence  the  movements  of  the  body.  But  the  power 
to  alter,  postpone,  or  entirely  inhibit,  nervous  movements 
is  but  a  part  of  the  general  work  ascribed  to  the  cerebrum 
as  the  organ  of  the  mind.  Numerous  experiments  per- 
formed upon  the  lower  animals,  together  with  observations 
on  man,  show  the  cerebrum  to  be  the  seat  of  the  mental 
activities,  and  to  make  possible,  in  some  way,  the  processes 
of  consciousness,  memory,  volition,  imagination,  emotion, 
thought,  and  sensation. 

Localization  of  Cerebral  Functions.  —  Many  experiments  have  been 
performed  with  a  view  to  determining  whether  the  entire  cerebrum  is 
concerned  in  each  of  its  several  activities  or  whether  special  functions 

belong  to  its  different  parts. 
These  experiments  have  been 
made  upon  the  lower  animals 
and  the  results  thus  obtained 
compared  with  observations 
made  upon  injured  and  im- 
perfectly developed  brains  in 
man.  The  results  have  led 
to  the  conclusion  that  certain 
forms  of  the  work  of  the  cere- 
brum are  localized  and  that 

FIG.  142. -Location  of  cerebral  func-  some  of  its  Parts  are  con- 
tions.  Diagram  of  cerebrum,  showing  most  cerned  in  processes  different 
of  the  areas  whose  functions  are  known.  from  those  of  others. 

The  work  of  locating  the 

functions  of  different  parts  of  the  cerebrum  forms  one  of  the  most 
interesting  chapters  in  the  history  of  brain  physiology.  The  portions 
having  to  do  with  sight,  voluntary  motion,  speech,  and  hearing  have 
been  rather  accurately  determined,  while  considerable  evidence  as  to 
the  location  of  other  functions  has  been  secured.  Much  of  the  cerebral 
surface, 'however,  is  still  undetermined  (Fig.  142). 

NERVOUS   CONTROL   OF   IMPORTANT   PROCESSES 

Circulation  of  the  Blood.  —  i.  Control  of  the  Heart.  —  The  ability  to 
contract  at  regular  intervals  has  been  shown  to  reside  in  the  heart 


fissure  of 
•SilviuS 


PHYSIOLOGY    OF   THE   NERVOUS    SYSTEM          319 

muscle.  Among  other  proofs  is  that  furnished  by  cold-blooded  animals, 
like  the  frog,  whose  heart  remains  active  for  quite  a  while  after  its  re- 
moval from  the  body.  These  automatic  contractions,  however,  are 
not  sufficient  to  meet  all  the  demands  made  upon  the  circulation.  The 
needs  of  the  tissues  for  the  constituents  of  the  blood  vary  with  their 
activity,  and  it  is  therefore  necessary  to  vary  frequently  the  force  and 
rapidity  of  the  heart's  contractions.  Such  changes  the  heart  itself  is 
unable  to  bring  about. 

For  the  purpose  of  controlling  the  rate  and  force  of  its  contractions, 
the  heart  is  connected  with  the  central  nervous  system  by  two  kinds  of 
fibers : 

a.  Fibers  that  convey  excitant  impulses  to  the  heart  to  quicken  its 
movements. 

b.  Fibers  that  convey  inhibitory  impulses  to  the  heart  to  retard  its 
movements. 

The  cell-bodies  of  the  excitant  fibers  are  found  in  the  sympathetic 
ganglia,  but  fibers  from  the  bulb  connect  with  and  control  them.  The 
cell-bodies  of  the  inhibitory  fibers  are  located  in  tlie  bulb,  from  where 
their  fibers  pass  to  the  heart  as  a  part  of  the  vagus  nerve. 

In  addition  to  the  fibers  above  mentioned,  are  those  that  convey 
impulses  from  the  heart  to  the  bulb.  These  connect  with  neurons  that 
in  turn  connect  with  blood  vessels  and  with  them  act  reflexively,  when 
the  heart  is  likely  to  be  overstrained,  to  cause  a  dilation  of  the  blood 
vessels.  This  lessens  the  pressure  which  the  heart  must  exert  to  empty 
itself  of  blood.  These  fibers  serve,  in  this  way,  as  a  kind  of  safety 
valve  for  the  heart. 

2.  Control  of  Arteries.  —  Changes  in  the  rate  and  force  of  the 
heart's  contractions  can  be  made  to  correspond  only  to  the  general 
needs  of  the  body.  When  the  blood  supply  to  a  particular  organ  is  to  be 
increased  or  diminished,  this  is  accomplished  through  the  muscular  coat 
in  the  arteries.  The  connection  of  the  arterial  muscle  with  the  sym- 
pathetic ganglia  and  the  method  by  which  they  vary  the  flow  of  blood  to 
different  organs  has  already  been  explained  (pages  311  and  49),  so  that 
only  the  location  of  the  controlling  neurons  need  be  noted  here.  These, 
like  the  controlling  neurons  of  the  heart,  have  their  cell-bodies  in  the 
bulb.  It  thus  appears  that  the  entire  control  of  the  circulation  is  effected 
in  a  reflex  manner  through  the  nerve  centers  in  the  bulb.  These  centers 
are  stimulated  by.  conditions  that  relate  to  the  movement  of  the  blood 
through  the  body. 


320  COORDINATION   AND    SENSATION 

Respiration.  —  Efferent  fibers  connect  the  different  muscles  of  respi- 
ration with  a  cluster  of  cell-bodies  in  the  bulb,  called  the  respiratory 
center.  This  center  together  with  the  nerves  and  muscles  in  question 
form  an  automatic,  or  self-acting,  mechanism  similar  in  some  respects 
to  that  of  the  heart.  Through  the  impulses  passing  from  the  respira- 
tory center  to  the  muscles,  a  rhythmic  action  is  maintained  sufficient  to 
satisfy  the  usual  needs  of  the  body  for  oxygen.  The  demand  of  the 
body  for  oxygen,  however,  varies  with  its  activities,  and  to  such  varia- 
tions the  respiratory  center  alone  is  unable  to  respond.  The  regulating 
factor  in  the  respiratory  movements  has  been  found  to  be  the  condition 
of  the  blood  with  reference  to  the  presence  of  oxygen  and  carbon  diox- 
ide. If  the  blood  contains  much  carbon  dioxide  and  little  oxygen,  it 
acts  as  a  strong  stimulus  to  the  respiratory  center,  causing  it,  in  turn, 
to  stimulate  the  respiratory  muscles  with  greater  intensity  and  fre- 
quency. On  the  other  hand,  if  the  blood  contains  much  oxygen  and 
little  carbon  dioxide,  it  acts  only  as  a  mild  stimulus.  This  explains 
how  physical  exercise  increases  the  breathing,  since  the  muscles  at 
work  consume  more  oxygen  than  when  resting  and  give  more  carbon 
dioxide  and  other  wastes  to  the  blood. 

The  respiratory  center  is  also  connected  by  afferent  nerves  with  the 
mucous  membrane  of  the  air  passages.  Irritation  of  the  nerve  endings 
in  this  membrane  causes  impulses  to  pass  to  the  center,  and  this  leads, 
by  reflex  action,  to  such  modifications  of  the  respiratory  acts  as  sneezing 
and  coughing.  There  is  also  a  connection  between  the  cerebrum  and 
the  respiratory  center.  This  is  shown  by  the  fact  that  one  can  volun- 
tarily change  the  rate  and  force  of  the  respiratory  movements,  and 
further  by  the  fact  that  emotions  affect  the  breathing. 
•  Regulation  of  the  Body  Temperature.  —  As  explained  in  the  study 
of  the  skin  (page  270),  the  nervous  system  regulates  the  body  temper- 
ature by  controlling  the  circulation  of  the  blood  through  the  skin  and 
the  internal  organs.  This  is  accomplished  by  stimulating  in  a  reflex 
manner  the  muscles  in  the  walls  of  certain  arteries.  To  prevent  the 
body  from  getting  too  hot,  muscles  in  the  arteries  going  to  the  skin 
relax,  thereby  allowing  more  blood  to  flow  to  the  surface,  where  the 
heat  can  be  disposed  of  through  radiation  and  through  the  evaporation 
of  the  perspiration.  On  the  other  hand,  if  the  body  is  in  danger  of 
losing  too  much  heat,  the  muscles  in  the  walls  of  arteries  going  to  the 
skin  are  made  to  contract  and  those  to  internal  organs  to  relax,  so  that 
less  blood  flows  to  the  skin  and  more  to  the  internal  organs.  In  this 


PHYSIOLOGY   OF   THE    NERVOUS    SYSTEM          321 

way  the  nervous  system  adjusts  the  circulation  to  suit  the  conditions  of 
temperature  outside  of  and  within  the  body  and,  in  so  doing,  maintains 
the  normal  body  temperature. 

Summary.  —  The  nervous  system  is  able  to  control,  co- 
ordinate, and  adjust  the  different  organs  of  the  body 
through  its  intimate  connection  with  all  parts  and  through 
a  stimulus  (the  nervous  impulse)  which  it  supplies  and 
transmits.  Nervous  impulses,  excited  by  external  stimuli, 
follow  definite  paths  and  cause  activity  in  the  different 
parts  of  the  body.  All  such  pathways  are  through  the 
central  nervous  system.  In  reflex  action  the  impulses 
are  mainly  through  the  spinal  cord,  but  to  some  extent 
through  the  bulb,  pons,  and  midbrain.  In  voluntary 
action  they  pass  through  the  cerebrum  —  a  condition  that 
leads  to  important  modifications  in  the  results.  The 
cerebrum,  in  addition  to  controlling  the  voluntary  move- 
ments, is  able  to  establish  the  necessary  conditions  for 
secondary  reflex  actions,  such  as  walking,  writing,  etc. 
Although  certain  of  the  divisions  of  the  nervous  system 
exercise  special  functions,  all  parts  of  it  are  closely 
related. 

Exercises.  —  i.    Give  the  function  of  each  of  the  parts  of  a  neuron. 

2.  State  the  purpose  of  the  nervous  impulse. 

3.  Show  that  the  exciting  cause  of  bodily  action  is  outside  of  the 
nervous  system  and,  to  a  large  extent,  outside  of  the  body. 

4.  Describe  the  arrangement  that  enables  stimuli  outside  of  the 
body  to  cause  action  within  the  body. 

5.  Describe  a  reflex  action  and  show  how  it  is  brought  about. 

6.  Distinguish  between  afferent,  efferent,  and  intermediate  neurons. 

7.  Draw  diagrams  showing  the  impulse  pathways  in  voluntary  and 
in  reflex  action. 

8.  What  purposes  are  served  by  the  sympathetic  neurons  ? 

9.  Describe  the  method  of  control  of  the  circulatory  and  digestive 
processes.     How  do  reflex  actions  protect  the  body  ? 


322 


COORDINATION    AND    SENSATION 


10.  Compare  voluntary  and  reflex  action.     In  what  sense  are  all  the 
activities  of  the  body  reflex  ? 

11.  In  what  sense  is  walking  voluntary  ?     In  what  sense  is  it  reflex? 

12.  How  does  secondary  reflex  action  lessen  the  work  of  the  nerv- 
ous system  ? 

13.  State  the  special  functions  of  the  nerves,  ganglia,  spinal  cord, 
bulb,  cerebellum,  and  cerebrum. 

14.    State    the    importance   of   the 

formation  of  correct  habits. 


PRACTICAL  WORK 

To  demonstrate  Nerve  Pathways.  — 
A  smooth  board,  2x6  ft.,  is  painted 
black,  and  upon  this  is  drawn  in  white 
a  life-size  outline  of  the  body.  Pieces 
of  cord  of  different  colors  and  lengths 
are  knotted  to  represent  mon-axonic 
and  di-axonic  neurons.  These  are 
then  pinned  or  tacked  to  the  board  in 
such  a  manner  as  to  'represent  the  con- 
nections in  the  different  kinds  of  nerve 
pathways.  Fig.  143  shows  such  a 
board  with  connections  for  a  reflex 
action  and  a  voluntary  action  of  the 
same  muscle. 

Study  of  the  "  Knee  Jerk  "  Reflex.  — 
A  boy  is  seated  on  a  chair  with  the 
legs  crossed.  With  a  small  pointer  he 
is  given  a  light,  quick  blow  on  the 
upper  margin  of  the  patella  at  the  point 
of  connection  of  the  tendon.  The 
stroke  will  usually  be  followed  by  a 
reflex  movement  of  the  foot.  Does 
this  take  place  independently  of  the 
mind  ?  (The  one  upon  whom  the  ex- 
periment is  being  performed  should 
assume  a  relaxed  condition  and  make 
no  effort  either  to  cause  or  prevent  the 
movement.)  Can  the  movement  be 


Fin.  143.  —  Nerve    board    for 
demonstrating  nerve  pathways. 


PHYSIOLOGY   OF   THE   NERVOUS    SYSTEM         323 

inhibited  (prevented)  ?  Repeat  the  experiment,  effort  being  made  to 
prevent  the  movement,  but  not  by  contracting  opposing  muscles. 

Other  reflex  actions  adapted  to  class  study  are  those  of  the  eyes, 
such  as  the  closing  of  the  lids  on  moving  objects  near  them  and  the 
dilating  of  the  pupils  when  the  eyes  are  shaded.  The  involuntary 
jerking  of  the  head  on  bringing  the  prongs  of  a  vibrating  tuning  fork  in 
contact  with  the  end  of  the  nose  is  also  a  reflex  action  which  can  be 
studied  to  advantage. 

To  determine  the  Reaction  Time.  —  Have  several  pupils  join  hands, 
facing  outwards,  making  a  complete  circle,  excepting  one  gap.  Give  a 
signal  by  touching  the  hand  of  one  pupil  at  the  end  of  the  line.  Let 
this  pupil  communicate  the  signal,  by  pressure  of  the  other  hand,  to  the 
next  pupil  and  so  on  around,  having  the  last  pupil  raise  the  free  hand 
at  close  of  the  experiment.  Note  carefully  the  time,  preferably  with  a 
stop  watch,  required  to  complete  the  experiment  and  divide  this  by  the 
number  of  pupils,  to  get  the  average  reaction  time.  The  experiment 
may  be  repeated  with  boys  only  and  then  with  girls,  comparing  their 
average  reaction  time. 

Reflex  Action  of  the  Salivary  Glands.  —  Place  a  small  pinch  of  salt 
upon  the  tongue  and  note  the  flow  of  saliva  into  the  mouth.  Try  other 
substances,  as  starch,  bits  of  wood,  and  sugar.  What  appears  to  be  the 
natural  stimulus  for  these  glands  ?  Compare  with  reflex  actions  of  the 
muscles. 


CHAPTER   XIX 
HYGIENE  OF  THE  NERVOUS  SYSTEM 

THE  far-reaching  effects  and  serious  nature  of  disorders 
of  the  nervous  system  are  sufficient  reasons  for  consider- 
ing carefully  those  conditions  that  make  or  mar  its  effi- 
ciency. Controlling  all  the  activities  of  the  body  and 
affecting  through  its  own  condition  the  welfare  of  all  the 
organs,  the  hygiene  of  the  nervous  system  is.  in  a  large 
measure,  the  hygiene  of  the  entire  body.  Moreover,  it  is 
known  that  some  of  our  worst  diseases,  including  paralysis 
and  insanity,  are  disorders  of  the  nervous  system  and  are 
prevented  in  many  instances  by  a  proper  mode  of  living. 

The  Main  Problem.  —  Many  of  our  nervous  disorders  are 
undoubtedly  due  to  the  age  in  which  we  live.  Our  modern 
civilization,  with  all  its  facilities  for  human  advancement 
and  enjoyment,  throws  an  extra  strain  upon  the  nervous 
system.  Educational  and  social  standards  are  higher  than 
ever  before  and  life  in  all  its  phases  is  more  complex.  Since 
we  can  hardly  change  the  conditions  under  which  we  live, 
and  probably  would  not  if  we  could,  we  must  learn  to  adapt 
or  adjust  ourselves  to  them  so  as  to  secure  for  the  nervous 
system  such  relief  as  it  requires.  This  adjustment  is 
sometimes  difficult,  even  when  the  actual  needs  of  the 
nervous  system  are  known. 

The  healthful  action  of  the  nervous  system  requires,  on 
the  one  hand,  exercise,  but  on  the  other  hand,  a  certain 
condition  of  quietude,  or  poise  —  a  state  which  is  directly 
opposed  to  that  of  restlessness.-  The  conditions  of  modern 

324 


HYGIENE   OF   THE   NERVOUS   SYSTEM  325 

life  seem  able  to  force  upon  the  nervous  system  all  the 
exercise  that  it  needs,  and  more  (whether  it  be  of  the  right 
kind  or  not),  so  that  the  main  problem  of  to-day  seems  to 
be  that  of  conserving,  or  economizing,  the  nervous  energy 
and  of  preventing  nervous  waste. 

Wasteful  Forms  of  Nervous  Activity.  —  There  are  with- 
out doubt  many  forms  of  activity  that  waste  the  vital  forces 
of  the  body  and  lead  to  nervous  exhaustion.  Take,  for  ex- 
ample, the  rather  common  habit  of  worrying  over  the  trivial 
things  of  life.  Certainly  the  nervous  energy  spent  in  this 
way  cannot  be  used  in  doing  useful  work,  but  must  be 
counted  as  so  much  loss  to  the  body.  One  who  would  use 
his  nervous  system  to  the  best  advantage  must  find  some 
way  of  preventing  waste  of  this  kind.1 

Undue  excitement,  as  well  as  pleasurable  dissipations, 
also  tend  toward  nervous  exhaustion.  And  while  the  fact 
is  recognized  that  pleasurable  activities  supply  a  necessary 
mental  exercise,  the  limit  of  healthful  endurance  must  be 
watched  and  excesses  of  all  kinds  avoided.  Intense 
emotional  states  are  found  to  be  exhausting  in  the  extreme ; 
and  the  suppression  of  such  undesirable  feelings  as  anger, 
fear,  jealousy,  and  resentment  are  of  immense  value  in  the 
hygiene  of  the  nervous  system. 

The  Habit  of  Self-control.  —  Much  of  the  needless  waste 
of  nervous  energy,  including  that  of  worrying  over  trivial 
matters,  may  be  prevented  through  the  exercise  of  self- 
control.  From  the  standpoint  of  the  nervous  system,  the 
present  age  differs  from  the  past  mainly  in  supplying  a 

1  Where  a  deep-seated  cause  for  worry  exists,  there  may  be  occasion  for  grave 
concern.  Many  people  have  become  insane  through  continued  worry  about  some 
one  thing.  In  cases  of  this  kind  the  sufferer  needs  the  aid  of  sympathetic  friends, 
and  sometimes  of  the  physician,  in  getting  the  mind  away  from  the  exciting  cause. 
A  change  of  scene,  a  visit,  or  some  new  employment  is  frequently  recommended, 
where  the  actual  cause  for  the  worry  cannot  be  removed. 


326  COORDINATION  AND   SENSATION 

greater  number  and  variety  of  nerve  stimuli.  Self-control 
means  the  ability  to  suppress  activities  that  would  result 
from  undesirable  stimuli  and  to  direct  the  bodily  activities 
into  channels  that  are  profitable.  Self-control,  therefore,  is 
not  only  to  be  exercised  on  occasions  of  great  emergency, 
but  in  the  everyday  affairs  of  life  as  well.  It  is  even  more 
important  that  the  daily  toiler  at  his  task  be  able  to  keep 
the  petty  annoyances  of  life  from  acting  as  irritants  to  his 
nervous  system  than  that  he  keep  cool  during  some  great 
calamity.  The  habit  of  self-control  is  acquired  mainly 
through  the  persistent  effort  to  prevent  any  and  all  kinds 
of  petty  annoyances  from  affecting  the  nerves  or  the 
temper. 

Nervousness. — Self-control  is  much  more  easily  prac- 
ticed by  some  than  by  others.  This  is  due  partly  to  habit, 
but  is  also  due  to  an  actual  difference  in  the  degree  of 
sensitiveness,  or  irritability,  of  the  nervous  systems  of  dif- 
ferent people.  One  whose  nervous  system  tends  to  respond 
too  readily  to  any  and  all  kinds  of  stimuli  is  said  to  be 
"  nervous."  This  condition  is  in  some  instances  inherited, 
but  is  in  most  cases  due  to  the  wasteful  expenditure  of 
nervous  energy  or  to  the  action  of  some  drug  upon  the 
body.  Excess  of  mental  work,  too  much  reading,  long- 
continued  anxiety,  eye  strain,  and  the  use  of  tea,  coffee, 
alcohol,  tobacco,  or  other  drugs,  including  many  of  those 
taken  as  medicines,  are  known  to  cause  nervousness. 
Nervousness  is  not  only  a  source  of  great  annoyance,  both 
to  one's  self  and  to  others,  but  is  a  menace  to  the  general 
health. 

The  first  step  toward  securing  relief  from  such  a  con- 
dition is  the  removal  of  the  cause.  The  habits  should  be 
inquired  into  and  excesses  of  all  kinds  discontinued.  In 
some  instances  it  may  be  necessary  to  have  the  eyes  exam- 


HYGIENE   OF   THE   NERVOUS   SYSTEM  327 

incd  and  glasses  fitted  by  a  competent  oculist.1  The 
nervous  energy  should  be  carefully  economized  and  the 
habit  of  self-control  diligently  cultivated.  Special  exer- 
cises that  have  for  their  purpose  the  equalizing  of  the  cir- 
culation and  the  strengthening  of  the  blood  vessels  of  the 
neck  and  the  brain  also  have  beneficial  effects. 

Nervous  Overstrain.  —  Both  mental  and  physical  over- 
work tends  to  weaken  the  nervous  system  and  to  produce 
nervousness.  Where  hard  mental  work  is  long  continued, 
or  where  it  is  carried  on  under  excitement,  a  tense  nervous 
condition  is  developed  which  is  decidedly  weakening  in  its 
effects.  The  causes  which  lead  to  such  a  condition,  and 
in  fact  overwork  of  all  kinds,  should  if  possible  be  avoided. 
Where  this  is  not  possible,  and  in  many  cases  it  is  not,  the 
period  of  overwork  should  be  followed  by  one  of  rest, 
recreation,  and  plenty  of  sleep.  To  the  overworked  in 
body  or  in  mind,  nothing  is  more  important  from  a  hygi- 
enic, as  well  as  moral,  standpoint,  than  the  right  use  of  the 
one  rest  day  in  seven.  The  best  interests  of  our  modern 
civilization  require  that  the  Sabbath -be  kept  as  a  quiet, 
rest-giving  day. 

Disturbed  Circulation  of  the  Brain.  —  Nervousness  not  in- 
frequently is  accompanied  by  an  increase  in  the  circulation 
of  the  brain  and  disappears  when  this  condition  is  relieved. 
Though  mental  work  and  excitement  tend  naturally  to  in- 
crease the  circulation  in  the  brain,  this  should  subside  with 
rest  and  relief  from  excitement.  When  there  is  a  tendency 

1  Any  part  of  the  body  which  is  overworked  or  which  works  at  a  disadvantage 
tends  to  disturb,  more  or  less,  the  entire  nervous  system  and  to  produce  nervous- 
ness. Especially  is  this  true  of  such  delicate  and  highly  sensitive  structures  as  the 
eyes.  If  the  eyes  do  not  focus  properly  or  if  the  muscles  that  move  the  eyeballs 
are  out  of  their  natural  adjustment,  extra  work  is  thrown  upon  these  delicate  parts. 
One  of  the  first  and  sometimes  the  only  indication  of  eye  strain  is  that  of  some  dis- 
turbance of  the  nervous  system.  For  this  reason  it  is  important  to  carefully  test 
the  eyes  in  determining  the  cause  of  nervousness  (page  385). 


328  COORDINATION   AND    SENSATION 

for  this  condition  to  become  permanent,  effort  should  be 
made  looking  for  relief.  Increasing  the  circulation  in  the 
lower  extremities  by  hot  or  cold  foot  baths,  or  by  much 
walking,  is  found  to  be  most  beneficial.  Special  exercises 
of  the  muscles  of  the  neck  are  also  recommended  as  a 
means  of  relieving  this  condition.1 

Hygienic  Value  of  Work.  —  Within  reasonable  limits, 
both  mental  and  physical  work  are  conducive  to  the  vigor 
of  the  nervous  system.  Through  work  the  energies  of  the 
body  find  their  natural  outlet,  and  this  prevents  dissipation 
and  the  formation  of  bad  habits.  Even  hard  work  does 
not  injure  the  nervous  system,  and  severe  mental  exertion 
may  be  undergone,  provided  the  proper  hygienic  conditions 
*'  are  observed.  The  nervous  disorders  suffered  by  brain 
workers  are  not,  as  a  rule,  due  to  the  work  which  the  brain 
does,  but  to  violation  of  the  laws  of  health,  especially  the 
law  of  exercise.  Such  persons  should  observe  the  general 
laws  of  hygiene  and  especially  should  they  practice  daily 
those  forms  of  physical  exercise  that  tend  to  counteract 
the  effects  of  mental  work. 

Physical  Exercise  properly  taken  is  beneficial  to  the 
nervous  system  through  both  direct  and  indirect  effects. 
A  large  proportion  of  the  nerve  cells  have  for  their  func- 
tion the  production  of  motion,  and  these  are  called  into 
play  only  through  muscular  activity.  Then,  as  already 
suggested,  physical  exercise  counteracts  the  unpleasant 
effects  of  mental  work.  Hard  study  causes  an  excess  of 
blood  to  be  sent  to  the  brain  and  a  diminished  amount 

1  One  form  of  neck  exercise  recommended  for  this  purpose  is  easily  taken  on 
retiring  at  night.  Lying  flat  on  the  back,  without  a  pillow,  lift  the  head  slowly  from 
the  bed  and  let  it  as  slowly  settle  back  to  the  level  of  the  body.  Repeat  several 
times,  lying  on  the  back,  and  then  again  on  the  face  and  again  on  each  side.  Prac- 
tice these  exercises  every  night  during  an  interval  of  a  month  or  until  relief  is 
secured. 


HYGIENE  OF   THE   NERVOUS   SYSTEM  329 

to  the  arms  and  to  the  legs.  Physical  exercise  redistributes 
the  blood  and  equalizes  the  circulation.  Light  exercise 
should,  therefore,  follow  hard  study.  The  student  before 
retiring  at  night  is  greatly  aided  in  getting  to  sleep  and  is 
put  in  a  better  condition  for  the  next  day's  work  by  ten  to 
fifteen  minutes  of  light  gymnastics.  A  daily  walk  of  two 
or  three  miles  is  also  an  excellent  means  of  counteracting 
the  effects  of  mental  work.  The  brain  worker  should, 
however,  avoid  violent  exercise  or  the  carrying  of  any  kind 
of  exercise  to  exhaustion. 

Sleep,  and  plenty  of  it,  is  one  of  the  first  requirements 
of  the  nervous  system.  It  is  during  sleep  that  the  ex- 
hausted brain  cells  are  replenished.  To  shorten  the  time 
for  sleep  is  to  weaken  the  brain  and  to  lessen  its  working 
force.  No  one  should  attempt  to  get  along  with  less  than 
eight  hours  of  sleep  each  day  and  most  people  require 
more.  Children  require  more  sleep  than  adults.  Those 
under  six  years  should  have  from  eleven  to  twelve  hours  of 
sleep  per  day.  Children  between  six  and  ten  years  should 
have  at  least  ten  hours. 

Insomnia,  or  sleeplessness,  on  account  of  its  effects  upon 
the  nefvous  system,  is  to  be  regarded  as  a  serious  con- 
dition, and  hygienic  means  for  relieving  it  should  be 
diligently  sought.  Having  its  cause  in  nervousness,  a 
disturbed  circulation  of  the  brain,  or  some  form  of  nervous 
exhaustion,  it  is  benefited  through  relieving  these  condi- 
tions and  in  the  manner  already  described.  Of  course  the 
external  conditions  for  aiding  sleep  should  not  be  over- 
looked. The  bed  should  be  comfortable,  and  the  room 
should  be  cool,  well  ventilated,  dark,  and  quiet.  The 
inducing  of  sleep  by  means  of  drugs  is  a  dangerous  prac- 
tice and  should  never  be  resorted  to  except  under  the 
direction  of  the  physician. 


330 


COORDINATION    AND    SENSATION 


Effects  of  Heat  and  Cold.  —  Heat  and  cold  both  have 
their  effects  upon  the  nervous  system.  Heat  increases 
the  nervous  irritability,  while  cold  acts  as  a  natural  seda- 
tive to  the  nerves.  A  nervous  person  is  made  more 
nervous  by  an  overheated  atmosphere,  but  derives  bene- 
ficial effects  from  exposing  the  body  freely  to  cold  air  and 
water.  The  tonic  cold  bath  (page  273),  if  taken  with  the 
usual  precautions,  can  be  used  to  good  advantage  in  di- 
minishing nervousness.  The  taking  of  outdoor  exercise 
in  cold  weather  is,  for  the  same  reason,  an  excellent 
practice. 

Effect  of  Emotional  States.  —  We  have  already  noted 
the  effect  of  certain  emotional  states  upon  the  digestion 
of  the  food  (page  162).  Emotional  states  are  also  known 
to  interfere  with  breathing  and  with  the  action  of  the 
heart.  Such  effects  are  explained  through  the  close  re- 
lation of  the  mind  to  the  work  of  the  nervous  system  in 
general.  While  certain  emotional  states,  such  as  fear, 
anger,  melancholia,  and  the  impulse  to  worry,  interfere 
seriously  with  the  normal  action  of  the  nervous  system, 
others,  such  as  contentment,  cheerfulness,  and  joy,  are 
decidedly  beneficial  in  their  effects.  How  important,  then, 
is  the  habit  of  suppressing  the  states  that  are  harmful  and 
of  cultivating  those  that  are  beneficial.  From  a  hygienic, 
as  well  as  social,  standpoint  a  cheerful,  happy  disposition 
is  worth  all  the  effort  necessary  for  its  attainment. 

The  Nervous  Condition  of  Children  should  be  a  matter  of 
deep  concern  on  the  part  of  both  parents  and  teachers. 
In  the  home,  as  well  as  in  the  school,  the  child  may  be 
"  pushed "  until  the  nervous  system  receives  permanent 
injury.  Exhaustion  of  nerve  cells  is  produced  through 
too  many  and  too  vivid  impressions  being  made  upon  the 
immature  brain.  The  child  should  be  protected  from 


HYGIENE   OF   THE    NERVOUS    SYSTEM  331 

undue  excitement.  He  should  have  the  benefit  of  outdoor 
exercise  and  should  be  early  inured  to  cold.  He  should 
be  shielded  from  the  poisoning  effects  of  tea,  coffee, 
tobacco,  alcohol,  and  other  drugs.  He  should  have 
impressed  upon  him  the  habit  of  self-control.  He  should 
not  be  indulged  in  foolish  caprices  or  whims,  but  should 
be  taught  to  be  content  with  plain,  wholesome  food  and 
with  the  simple  forms  of  enjoyment. 

Influences  at  School.  —  School  life  is  necessarily  a  great 
strain  upon  the  child.  Night  study  added  to  the  work 
of  the  day  makes  a  heavy  burden  for  elementary  pupils  to 
bear.  Though  the  legal  school  age  is  usually  fixed  at  six 
years,  delicate  children  should  be  kept  out  of  school  until 
they  are  seven  or  eight  years  old,  provided  they  have  good 
homes.  In  addition  to  the  excitation  incident  to  studying 
and  reciting  lessons,  condition's  frequently  arise  both  in 
the  schoolroom  and  upon  the  playground  .that  create  a 
feeling  of  fear  or  dread  in  the  minds  of  children.  Quar- 
rels and  feuds  among  the  children  and  the  bullying  of  big 
boys  on  the  playground  may  work  untold  harm.  All  con- 
ditions tending  to  develop  fear,  uneasiness,  or  undue 
excitement  on  the  part  of  children  should  receive  the 
attention  of  those  in  authority. 

Excessive  Reading  is  a  frequent  cause  of  injury  to  the 
nervous  systems  of  children.  This  has  a  bad  effect,  both 
on  account  of  too  many  impressions  being  made  upon 
the  mind  and  also  on  account  of  the  strain  to  the  eyes. 
Then  if  the  reading  consists  mostly  of  light  fiction,  the 
mind  is  directed  away  from  the  really  important  things  of 
life.  The  reading  of  children  should  be  thoughtfully  con- 
trolled, both  as  to  quality  and  quantity.  Exciting  stories 
should,  as  a  rule,  be  excluded,  but  a  taste  for  biography, 
historical  and  scientific  writings,  and  for  the  great  works 


332  COORDINATION    AND    SENSATION 

of  literature  should  be  cultivated.  Simple  fairy  tales  which 
have  a  recognized  value  in  developing  the  imagination  of 
the  child  need  not  be  omitted,  but  it  is  of  vital  importance 
that  the  "  story -reading  habit "  be  not  formed. 

Effects  of  Drugs.  —  Because  of  its  delicacy  of  structure  a 
number  of  chemical  compounds,  or  drugs,  are  able  to  pro- 
duce injurious  effects  upon  the  nervous  system.  Some  of 
these  are  violent  poisons,  while  others,  in  small  quantities, 
are  mild  in  their  action.  Certain  drugs,  in  addition  to  their 
immediate  effects,  bring  about  changes  in  the  nervous 
system  which  cause  an  unnatural  appetite,  or  craving,  that 
leads  to  their  continued  use.  This  is  the  case  with  alcohol, 
the  intoxicating  substance  in  the  usual  saloon  drinks,  and 
with  nicotine,  the  stimulating  drug  in  tobacco.  The  same 
is  also  true  of  morphine,  chloral,  and  several  other  drugs 
used  as  medicines.  The  danger  of  becoming  a  slave  to 
some  useless  and  pernicious  habit  should  dissuade  one  from 
the  use  of  drugs  except  in  cases  of  positive  emergency. 

Alcohol  and  the  Nervous  System.  —  Alcohol,  as  already 
shown,  injures  practically  all  portions  of  the  body;  but  it 
has  its  worst  effects  upon  the  nervous  system.  Through 
its  action  on  this  system,  it  interferes  with  the  circulation 
of  the  blood,  produces  a  condition  of  "  temporary  insanity  " 
called  intoxication,  weakens  the  will,  and  eventually  de- 
thrones the  reason.  Worst  of  all,  it  produces  a  condition 
of  "chronic  poisoning"  which  manifests  itself  in  an  un- 
natural craving,  and  this  causes  it  to  be  used  by  the  victim 
even  when  he  knows  he  is  "  drinking  to  his  own  destruc- 
tion." Though  its  use  in  small  quantities  does  not,  as  a 
rule,  produce  such  marked  effects  upon  the  nervous  system, 
it  develops  the  "craving,"  and  this  is  apt  in  time  to  lead 
to  its  use  in  larger  quantities.  But  even  if  this  does  not 
occur,  the  practice  is  objectionable  for  its  unhygienic  effects 


HYGIENE  OF  THE   NERVOUS   SYSTEM  333 

•in  general.1  Tippling  with  such  mild  solutions  of  alcohol 
as  light  wine,  beer,  and  hard  cider  is,  for  these  reasons,  a 
dangerous  pastime. 

Alcohol  and  Crime.  —  It  is  sometimes  stated  that  no  one 
who  leaves  alcohol  alone  will  be  injured  by  it.  This  is 
true  only  of  its  direct  effects;  not  of  its  indirect  effects. 
Whenever  a  crime  is  committed  somebody  is  injured,  and 
alcohol  is  known  to  be  a  chief  cause  of  crime.  Alcohol 
causes  crime  through  the  loss  of  self-control,  seen  espe- 
cially in  intoxication,  and  also  because  of  the  moroseness 
and  quarrelsomeness  which  it  developes  in  certain  individ- 
uals. Indirectly  it  causes  crime  through  the  poverty 
which  it  engenders  and  through  its  influence  in  bringing 
about  social  conditions  out  of  which  crime  develops. 
Everything  considered,  the  free  use  of  alcohol  is  incom- 
patible with  the  nervous  health  and  moral  tone  of  a 
community. 

Nicotine  and  the  Nervous  System.  —  Nicotine  is  an  oily 
substance  which  is  extracted  from  the  tobacco  plant.  Its 
action  on  the  nervous  system  is  in  general  that  of  a  poison. 
Taken  in  small  quantities,  it  is  a  mild  stimulant  and,  if  the 
doses  are  repeated,  a  habit  is  formed  which  is  difficult  to 
break..  Tobacco  is  used  mainly  for  the  stimulating  effect  of 
this  drug.  While  not  so  serious  in  its  results  as  the  alcohol 
and  other  drug  habits,  the  use  of  tobacco  is  of  no  benefit, 
is  a  continual  and  useless  expense,  and,  in  many  instances, 
causes  a  derangement  of  the  healthy  action  of  the  body.2 

1  Insurance  statistics  show  that  habitual  moderate  drinkers  do  not  live  so  long 
as  abstainers. 

2  Organs  very  frequently  affected  by  tobacco  are  the  heart  and  the  eyes.     It  in- 
duces, as  already  stated  (page  56) ,  a  dangerous  nervous  derangement  called  "  tobacco 
heart,"  and   it  causes  a  serious  disorder  of  the  retina  (retinitis)  which  leads  in 
some  instances  to  loss  of  vision.    Tobacco  smoke  also  acts  as  an  irritant  to  the 
delicate  lining  of  the  eyes,  especially  when  the  tobacco  is  smoked  indoors. 


334  COORDINATION   AND   SENSATION 

With  the  bad  effects  of  the  nicotine  must  be  included  those* 
of  questionable  substances  added  to  the  tobacco  by  the  manu- 
facturer, either  for  their  agreeable  flavor  or  for  adulteration. 

Relation  of  Age  to  the  Effects  of  Nicotine.  —  The  use  of 
tobacco  by  the  young  is  especially  to  be  deplored.  In 
addition  to  the  harmful  effects  observed  in  those  of  mature 
years,  nicotine  interferes  with  the  normal  development  of 
the  body  and  lays,  in  many  instances,  the  foundation  for 
physical  and  mental  weakness  in  later  life.  The  cigarette 
is  decidedly  harmful,  especially  when  inhalation  is  practiced, 
its  deadening  effects  being  in  part  due  to  the  wrappers, 
some  of  which  have  been  shown  to  contain  arsenic  and 
other  poisonous  drugs.  While  dulling  the  intellect  and 
weakening  the  body,  cigarette  smoking  also  tends  to  make 
criminals  of  boys.1  Parents,  teachers,  school  officers,  and  all 
who  have  the  good  of  mankind  at  heart  should  take  every 
precaution,  including  that  of  setting  a  good  example,  to 
prevent  the  formation  of  the  tobacco  habit  by  those  of 
immature  years. 

Habit  versus  Self-control.  —  The  power  of  self-control, 
already  emphasized  for  its  importance  in  the  economical 
expenditure  of  the  nervous  energy,  is  of  vital  importance 
in  its  relation  to  the  habits  of  the  body.  Self-control,  is  the 
chief  safeguard  against  the  formation  of  bad  habits  and  is 
the  only  means  of  redemption  from  such  habits  after  they 
have  once  been  formed.  The  persistent  cultivation  of  the 
power  to  control  the  appetites  and  the  passions,  as  well  as 
all  forms  of  activity  which  tend  to  injure  the  body  or  de- 
base the  character,  gives  a  tone  to  the  nervous  system 

1  Of  4117  boys  in  the  Illinois  State  Reformatory,  4000  used  tobacco,  and  over 
3000  were  cigarette  smokers.  Dr.  Hutchison,  of  the  Kansas  State  Reformatory, 
says :  "  Using  cigarettes  is  the  cause  of  the  downfall  of  more  of  the  inmates  of  this 
institution  than  all  other  vicious  habits  combined." 


HYGIENE   OF   THE   NERVOUS   SYSTEM  335 

which  increases  the  self-respect  and  raises  the  individual  to 
a  higher  plane  of  life.  The  worst  habits  can  be  broken 
and  good  ones  formed  in  their  stead,  if  only  there  is  suf- 
ficient determination  to  accomplish  these  results.  Failure 
comes  from  not  having  the  mind  thoroughly  "  made  up  " 
and  from  not  having,  back  of  the  desire  to  do  better,  "  the 
strong  will  of  a  righteous  determination." 

Effects  of  External  Conditions.  —  While  the  inner  life 
and  habits  have  most  to  do  with  the  hygiene  of  the  nerv- 
ous system,  a  certain  amount  of  attention  may  properly 
be  given  to  those  conditions  outside  of  the  body  which 
affect  directly  or  indirectly  the  state  of  this  system. 
Noise,  disorder,  and  confusion  act  as  nervous  irritants, 
but  quiet,'  order,  and  system  have  the  opposite  effect. 
There  is,  therefore,  much  in  the  management  of  the  office, 
factory,  schoolroom,  or  home  that  has  to  da  with  the  real 
hygiene  of  the  nerves  as  well  as  with  the  efficiency  of  the 
work  that  is  being  done.  The  suppression  of  distracting 
influences  not  only  enables  the  mind  to  be  given  fully  to 
the  work  in  hand,  but  actually  prevents  waste  of  nervous 
energy.  Although  the  responsibility  for  securing  the  best 
conditions  for  work  rests  primarily  with  those  in  charge, 
it  is  also  true  that  each  individual  in  every  organization 
may  contribute  to  the  order  or  disorder  that  prevails. 

Social  Relations.  —  In  considering  the  external  conditions 
that  affect  the  nervous  system,  the  fact  must  not  be  over- 
looked that  man  is  a  social  being  and  has  to  adjust  himself  to 
an  established  social  order.  His  relations  to  his  fellow-men, 
therefore,  affect  strongly  his  nervous  condition  and  theirs 
also.  For  this  reason  the  best  hygiene  of  the  nervous  sys- 
tem is  based  upon  moral  as  well  as  physical  right  living. 
Along  with  the  power  of  self-control  and  the  maintenance 
of  a  correct  nervous  poise,  there  should  be  a  proper  regard 


336  COORDINATION    AND    SENSATION 

for  the  welfare  of  others.  On  account  of  the  ease  with  which 
one  individual  may  disturb  the  nervous  state  of  another,  those 
social  forms  and  customs  which  tend  to  establish  harmoni- 
ous relations  among  men  are  truly  hygienic  in  their  effects, 
and  may  well  be  carried  out  in  spirit  as  well  as  "in  letter." 

It  is  also  a  fact  that  a  given  mental  state  in  one  person 
tends  to  excite  a  like  state  in  those  with  whom  he  asso- 
ciates. How  important,  then,  that  each  and  all  cultivate, 
as  habits,  the  qualities  of  cheerfulness,  kindness,  and 
good-will,  instead  of  the  opposrte  states  of  mind.  Espe- 
cially in  the  family,  and  other  groups  of  closely  associated 
individuals,  should  the  nervous  effect  of  one  member  upon 
the  others  be  considered  and  every  effort  made  to  secure 
and  maintain  harmonious  relations. 

The  High  Ideal.  —  Everything  considered,  the  conditions 
most  favorable  to  the  healthfulness  of  the  nervous  system 
are  in  harmony  with  what  our  greatest  teachers  have 
pointed  to  as  the  higher  plane  of  living.  On  this  account 
a  true  conception  of  the  value  and  meaning  of  life  is  of 
the  greatest  importance.  An  ever  present,  strong  desire  to 
live  a  vigorous,  but  simple  and  noble,  life  will  suggest  the 
proper  course  to  pursue  when  in  doubt  and  -will  stimulate 
the  power  of  self-control.  It  will  lead  to  the  stopping  of 
"  nerve  leaks "  and  to  the  maintenance  of  harmonious 
relations  with  one's  fellows.  It  will  cause  one  to  recoil 
from  the  use  of  alcohol  and  other  nerve  poisons,  as  from 
a  deadly  serpent,  seeing  the  end  in  the  beginning,  and 
will  be  the  means  eventually  of  leading  the  body  into  its 
greatest  accomplishments. 

Summary.  —  The  nervous  system,  on  account  of  its 
delicate  structure,  is  liable  to  injury  through  wrong 
methods  of  using  it  and  also  through  the  introduction  of 
drugs,  or  poisons,  into  the  body.  There  are  also  found 


HYGIENE   OF   THE   NERVOUS   SYSTEM  3.37 

in  our  methods  of  living  and  systems  of  education  condi- 
tions that  tend  to  waste  the  nervous  energy.  To  protect 
the  nervous  system  from  all  these  threatened  dangers 
requires,  among  other  things,  the  power  of  self-control. 
This  enables  the  individual  to  direct  his  life  according  to 
his  highest  ideals  and  to  free  himself  from  habits  known 
to  be  injurious.  Children  must  have  their  nervous  systems 
safeguarded  by  parents  and  teachers.  Especially  must 
they  be  kept  from  becoming  enslaved  to  some  drug,  such 
as  alcohol  or  the  nicotine  of  tobacco. 

Exercises.  —  i.    In  what  respect  is  the  hygiene  of  the  nervous  sys- 
tem the  hygiene  of  the  entire  body  ? 

2.  Of  what  value  in  the  hygiene  of  the  nervous  system  is  the  power 
of  self-control  ?     How  is  the  habit  of  self-control  formed  ? 

3.  Name  several  forms  of  activity  that  waste  the  nervous  energy. 

4.  Name  several  influences  that  react  unfavorably  on  the  nervous 
systems  of  children. 

5.  How   may  too  much  reading  prove   injurious  to  the  nervous 
system? 

6.  What  forms  of  physical   exercise  are   beneficial  to  the  brain 
worker  ? 

7.  Why  is  the  use  of  alcohol  even  in  small  quantities  to  be  re- 
garded as  a  dangerous  practice  ? 

8.  Name  several  causes  of  nervousness. 

9.  What  are  the  unanswerable  arguments  for  preventing  the  use 
of  tobacco  by  the  young  ? 

10.  Why  do  cigarettes  have  a  more  harmful  effect  upon  the  body 
than  other  forms  of  tobacco  ? 

1 1 .  Enumerate  conditions  in  the  schoolroom  that  dissipate  the  nerv- 
ous energy  of  pupils  ;  that  economize  it. 


CHAPTER   XX 
PRODUCTION  OF  SENSATIONS 

OUR  study  of  the  nervous  system  has  shown  that 
impulses  arising  at  the  surface  of  the  body  are  able, 
through  connecting  neurons,  to  bring  about  various 
activities.  Moving  along  definite  pathways,  they  induce 
motion  in  the  muscles,  and  in  the  glands  the  secretion  of 
liquids.  It  is  now  our  purpose  to  consider  the  effect  pro- 
duced by  afferent  impulses  upon  the  brain  and,  through 
the  brain,  upon  the  mind.1  This  effect  is  manifested  in  a 
variety  of  similar  forms,  known  as 

The  Sensations.  —  Sensations  constitute  the  lowest 
forms  of  mental  activity.  Roughly  speaking,  they  are  the 
states  of  mind  experienced  as  the  direct  result  of  impulses 
reaching  the  brain.  In  a  sense,  just  as  impulses  passing 
to  the  muscles  cause  motion,  impulses  passing  to  the 
brain  cause  sensations.  The  feeling  which  results  from 
the  hand's  touching  a  table  is  a  sensation  and  so  also  is  the 
pain  which  is  caused  by  an  injury  to  the  body.  The  men- 
tal action  in  each  case  is  due  to  impulses  passing  to  the 
brain.  Care  must  be  exercised  by  the  beginner,  however, 
not  to  confuse  sensations  with  the  nervous  impulses,  on  the 
one  hand,  or  with  secondary  mental  effects,  such  as  emotion 
or  imagination,  on  the  other.  Sensations  are  properly 
regarded  as  the  first  conscious  effects  of  the  afferent 
impulses  and  as  the  beginning  stage  in  the  series  of  mental 
processes  that  may  take  place  on  account  of  them. 

iThe  term  "mind"  is  used  in  this  and  preceding  chapters  in  its  popular,  not 
technical,  sense. 

338 


PRODUCTION   OF   SENSATIONS 


339 


In  some  way,  not  understood,  the  mind  associates  the 
sensation  with  the  part  of  the  body  from  which  the  im- 
pulses come.  Pain,  for  example,  is  not  felt  at  the  brain 
where  the  sensation  is  produced,  but  at  the  place  where 
the  injury  occurs.  This  association,  by  the  mind,  of  the 
sensations  with  different  parts  of  the  body,  is  known  as 
"  localizing  the  sensation." 

Sensation  Stimuli.  —  While  the  sensations  are  dependent 
upon  the  afferent  impulses,  the  afferent  impulses  are  in 
turn  dependent  upon  causes  outside  of  the  nervous  system. 
If  these  are  removed,  the  sensations  cease  and  they  do  not 
start  up  again  unless  the  exciting  influences  are  again 
applied.  Any  agency,  such  as  heat  or  pressure,  which, 
by  acting  on  the  neurons  of  the  body,  is  able  to  produce  a 
sensation,  may  be  called  a  sensation  stimulus.  It  has  per- 
haps already  been  observed  that  the  stimuli  that  lead  to 
voluntary  action,  as  well  as  those  that  produce  reflex  action 
of  the  muscles,  cause  sensations  at  the  same  time.  From 
this  we  may  conclude  that  sensation  stimuli  are  the  same 
in-  character  as  those  that  excite  motion.  On  the  other 
hand,  it  should  be  noted  that  sensations  are  constantly 
resulting  from  stimuli  that  are  of  too  mild  a  nature  to 
cause  motion. 

Classes  of  Sensations.  —  Perhaps  as  many  as  twenty  dis- 
tinct sensations,  such  as  pain,  hunger,  touch,  etc.,  are 
recognized.  If  these  are  studied  with  reference  to  their 
origin,  it  will  be  seen  that  some  of  them  result  from  the 
action  of  definite  forms  of  stimuli  upon  the  neurons  ter- 
minating in  sense  organs  ;  while  the  others,  as  a  rule,  arise 
from  the  action  of  indefinite  stimuli  upon  neurons  in  parts 
of  the  body  that  do  not  possess  sense  organs.  The  mem- 
bers of  the  first  class  —  and  these  include  the  sensations  of 
touch,  temperature,  taste,  smell,  hearing,  and  sight  — are 


340  COORDINATION    AND    SENSATION 

known  as  the  special  sensations.  The  others,  including 
the  sensations  of  pain,  hunger,  thirst,  nausea,  fatigue, 
comfort,  discomfort,  and  those  of  disease,  are  known  as 
organic,  or  general,  sensations.  These  two  classes  of  sen- 
sations differ  in  their  purpose  in  the  body  as  well  as  in  the 
manner  of  their  origin. 

Purposes  of  Sensations.  — '.Any  given  sensation  is  related 
to  the  stimulus  which  excites  it  as  an  effect  to  a  cause.  It 
starts  up  or  stops,  increases  in  intensity  or  diminishes, 
according  to  the  action  of  the  exciting  stimulus.  As  the 
stimuli  are  outside  of  the  nervous  system,  and  in  the 
majority  of  cases  outside  of  the  body,  the  sensations  in- 
dicate to  the  mind  what  is  taking  place  either  in  the  body 
itself  or  in  its  surroundings.  They  supply,  in  other  words, 
the  means  through  which  the  mind  acquires  information. 
By  means  of  the  special  sensations,  a  knowledge  of  the 
physical  surroundings  of  the  body  is  gained,  and  through 
the  organic  sensations  the  needs  of  the  body  and  the  state  of 
the  various  organs  are  indicated.  In  general,  sensations  are 
made  to  serve  two  great  purposes  in  the  body,  as  follows : 

1.  They  provide  the  necessary  conditions  for  intelligent 
and  purposeful  action  on  the  part  of  the  body. 

2.  They  supply  the  basis  for  the  higher  mental  activi- 
ties, as   perception,    memory,  thought,    imagination,    and 
emotion. 

Intelligent  action  is  impossible  without  a  knowledge 
both  of  the  bodily  organs  and  of  the  body's  surroundings. 
Protection  and  the  regulation  of  the  work  of  an  organ 
necessitate  a  knowledge  of  its  condition,  while  the  adapt- 
ing and  adjusting  of  the  body  to  its  surroundings  require 
a  knowledge  of  what  those  surroundings  are.  The 
dependence  of  all  the  higher  forms  of  mental  activity  upon 
sensations  is  recognized  by  psychologists  and  is  easily 


PRODUCTION   OF   SENSATIONS  341 

demonstrated  by  a  study  of  the  manner  in  which  we 
acquire  knowledge.  "Without  sensation  there  can  be  no 
thought." 

Steps  in  the  Production  of  Sensations.  —  The  steps  in  the 
production  of  sensations  are  not  essentially  different  from 
those  in  the  production  of  reflex  action/  First  of  all, 
external  stimuli  act  upon  the  fiber  terminations  in  the 
sense  organs,  or  elsewhere,  starting  impulses  in  the 
neurons.  These  pass  into  the  central  nervous  system  and 
there  excite  neurons  which  in  turn  discharge  impulses 
into  the  cerebrum.  The  result  is  to  arouse  an  activity  of 
the  mind  —  a  sensation.  The  steps  in  the  production  of 
any  special  sensation  naturally  involve  the  following  parts  : 

1.  A  sense  organ  where  the  terminations  of  the  neurons 
are  acted  upon  by  the  stimulus. 

2.  A  chain  of  neurons  which  connect  the  sense  organ 
with  the  brain. 

3.  The  part  of  the  cerebrum  which  produces  the  sen- 
sation. 

Sense  Organs.  —  The  sense  organs  are  not  parts  of  the 
afferent  neurons,  but  are  structures  of  various  kinds,  in 
which  the  neurons  terminate.  Their  function  is  to  enable 
the  sensation  stimuli  to  start  the  impulses.  By  directing, 
concentrating,  or  controlling  the  stimuli,  the  sense  organs 
enable  them  to  act  to  the  best  advantage  upon  the  neurons. 
When  it  is  recognized  that  such  widely  different  forces  as 
light  waves,  sound  waves,  heat,  pressure,  and  odors  are 
enabled  by  them  to  stimulate  neurons,  the  importance  of 
these  organs  becomes  apparent.  As  would  naturally  be 
inferred,  the  construction  of  any  sense  organ  has  particular 
reference  to  the  nature  of  the  stimulus  which  it  is  to  re- 
ceive. This  is  most  apparent  in  the  sense  organs  of  sight 
and  hearing. 


342 


COORDINATION   AND   SENSATION 


Simple  Forms  of  Sense  Organs.  —  The  simplest  form  of 
a  sense  organ  (if  such  it  may  be  called)  is  one  found  among 
the  various  tissues.  It  consists  of  the  terminal  branches 
of  nerve  fibers  which  spread  over  a  small  area  of  cells,  as 
a  network  or  plexus.  Such  endings  are  numerous  in  the 
skin  and  muscles. 

Next  in  order  of  complexity  are  the  so-called  end-bulbs. 
These  consist  of  rounded,  or  elongated,  connective  tissue 
capsules,  within  which  the  nerve  fibers  terminate.  On  the 
inside  the  fibers  lose  their  sheaths  and  divide  into  branches, 
which  wind  through  the  capsule.  End-bulbs  are  abundant 
in  the  lining  membrane  of  the  eye, 
and  are  found  also  in  the  skin  of  the 
lips  and  in  the  tissues  around  the 
joints. 

Slightly  more  complex  than  the 
end-bulbs  are  the  touch  corpuscles. 
These  are  elongated  bulb-like  bodies, 
having  a  length  of  about  one  three- 
hundredth  of  an  inch,  and  occupying 
the  papillae  of  the  skin  (Fig.  144). 
They  are  composed  mainly  of  connec- 
tive tissue.  Each  corpuscle  receives 
the  termination  of  one  or  more  nerve 
fibers.  These,  on  entering,  lose  the 
medullary  sheath  and  separate  into  a  number  of  branches 
that  penetrate  the  corpuscle  in  different  directions. 

The  largest  of  the  simple  forms  of  sense  organs  are 
bodies  visible  to  the  naked  eye  and  called,  from  their  dis- 
coverer Pacini,  the  Pacinian  corpuscles.  They  lie  along 
the  course  of  nerves  in  many  parts  of  the  body,  and  have 
the  general  form  of  grains  of  wheat.  (See  Practical  Work.) 
The  Pacinian  corpuscles  are  composed  of  connective  tissue 


FIG.  144.  —  A  touch 
corpuscle  highly  magni- 
fied. (See  text.) 


PRODUCTION   OF   SENSATIONS 


343 


arranged  in  separate  layers  around  a  narrow  central  cavity 
called  the  core  (Fig.  145).  Within  the  core  is  the  termina- 
tion of  a  large  nerve  fiber.  These  corpuscles  are  found  in 
the  connective  tissue  beneath 
the  skin,  along  tendons,  around 
joints,  and  among  the  organs 
of  the  abdominal  cavity. 

The  simple  forms  of  sense  E 
organs  have  a  more  or  less 
general  distribution  over  the 
body,  and  are  concerned  in 
the  production  of  at  least  three 
special  sensations.  These  are 
touch,  temperature,  and  the 
muscular  sensation. 

Touch,  or  feeling,  is  perhaps  A 
the  simplest  of  the  sensations. 
The  sense  organs  employed 
are  the  touch  corpuscles,  and 
the  external  stimulus  is  some 
form  of  pressure  or  impact. 
Pressure  applied  to  the  skin, 
by  acting  on  the  fiber  terminations  in  the  corpuscles,  starts 
the  impulses  that  give  rise  to  the  sensation.  The  touch 
corpuscles  render  the  fiber  terminations  so  sensitive  that 
the  slightest  pressure  is  able  to  arouse  sensations  of  touch. 
It  is  found  that  a  change  of  pressure,  rather  than  pressure 
that  is  constant,  is  the  active  stimulus.  That  all  parts  of 
the  skin  are  not  equally  sensitive  to  pressure,  and  that  the 
mind  does  not  interpret  equally  well  the  sensations  from 
different  parts,  are  facts  easily  demonstrated  by  experiment. 
(See  Practical  Work.) 

The  Temperature  Sensation.  —  Temperature  sensations, 


FIG.  145.  —  Pacinian  corpuscle, 
magnified.  A.  Medullated  nerve 
fiber.  B.  Axis  cylinder  terminating 
in  small  bulb  at  C.  D.  Concentric 
layers  of  connective  tissue.  E.  In- 
ner bulb. 


344  COORDINATION    AND   SENSATION 

like  those  of  touch,  are  limited  almost  entirely  to  the  skin. 
They  are  of  two  kinds,  and  are  designated  as  heat  sensa- 
tions and  as  cold  sensations.  Whether  the  sense  organs 
for  temperature  are  different  from  those  of  touch  is  not 
known.  It  is  known,  however,  that  the  same  corpuscles 
do  not  respond  alike  to  heat,  cold,  and  pressure. 

A  Change  of  Temperature,  rather  than  any  specific  degree 
of  heat  or  cold,  is  the  active  temperature  stimulus.  The 
sensation  of  warmth  is  obtained  when  the  temperature  of 
the  skin  is  being  raised,  and  of  cold  when  it  is  being  low- 
ered. This  explains  why  in  going  into  a  hallway  from  a 
heated  room  one  receives  a  sensation  of  cold,  while  in  com- 
ing into  the  same  hallway  from  the  outside  air  he  receives 
a  sensation  of  warmth.  It  is  for  the  same  reason  that  we 
are  able  to  distinguish  only  the  relative,  not  the  actual, 
temperature  of  bodies. 

Muscular  Sensations. — These  are  sensations  produced 
by  impulses  arising  at  the  muscles.  Such  impulses  origi- 
nate at  the  fiber  terminations  which  are  found  in  both  the 
muscles  and  their  tendons.  By  muscular  sensations  one  is 
conscious  of  the  location  of  a  contracting  muscle  and  of 
the  degree  of  its  tension.  They  also  make  it  possible  to 
judge  of  the  weight  of  objects. 

The  Sensation  of  Taste.  —  The  sense  organs  of  taste  are 
found  chiefly  in  the  mucous  membrane  covering  the  upper 
surface  of  the  tongue.  Scattered  over  this  surface  are  a 
number  of  rounded  elevations,  or  large  papillae  (A,  Fig. 
146).  Toward  the  back  of  the  tongue  two  rows  of  these, 
larger  than  the  others,  converge  to  meet  at  an  angle,  where 
is  located  a  papilla  of  exceptional  size.  Surrounding  each 
papilla  is  a  narrow  depression,  within  which  are  found  the 
sense  organs  of  taste  (B,  Fig.  146).  These  are  called,  from 
their  shape,  taste  buds,  and  each  bud  contains  a  central 


PRODUCTION   OF    SENSATIONS  345 

cavity  which  communicates  with  the  surface  by  a  small 
opening  —  the  gustatory  pore.  Within  this  cavity  are  many 
slender,  spindle-shaped  cells  which  terminate  in  hair-like 
projections  at  the  end  nearest  the  pore,  but  in  short  fibers 
at  the  other  end.  Nerve  fibers  enter  at  the  inner  ends  of 
the  buds  and  spread  out  between  the  cells  (C,  Fig.  146). 


~.  ex 


FIG.  146.  —  Sense  organs  of  taste.  A.  Map  of  upper  surface  of  tongue, 
showing  on  the  left  the  different  kinds  of  papillae,  and  on  the  right  the  areas  of 

taste  (after  Hall).     Area  sensitive  to  bitter  ( );    to  acid  ( ); 

to  salt  ( );    to  sweet  ( ).     B.   Section  through  a 

papilla,  n.  Small  nerve  connecting  with  taste  buds  at  d.  e.  Epithelium. 
C.  Single  taste  bud  magnified,  n.  Nerve,  the  fibers  of  which  terminate 
between  the  spindle-shaped  cells  a.  e.  Epithelial  cells. 

These  fibers  pass  to  the  brain  as  parts  of  two  pairs  of 
nerves  —  those  from  the  front  of  the  tongue  joining  the 
trigeminal  nerve,  and  those  from  the  back  of  the  tongue, 
the  glossopharyngeal  nerve. 

The  gustatory,  or  taste  stimulus,  is  some  chemical  or 
physical  condition  of  substances  which  is  manifested  only 
when  they  are  in  a  liquid  state.  For  this  reason  only  liquid 
substances  can  be  tasted.  Solids  to  be  tasted  must  first  be 
dissolved. 


346 


COORDINATION   AND   SENSATION 


The  different  taste  sensations  are  described  as  bitter, 
sweet,  sour,  and  saline,  and  in  the  order  named  are  recog- 
nized as  the  tastes  of  quinine,  sugar,  vinegar,  and  salt.  As 
to  how  these  different  tastes  are  produced,  little  is  known. 
Flavors  such  as  vanilla  and  lemon,  and  the  flavors  of  meats 
and  fruits,  are  really  smelled  and  not  tasted.  Taste  serves 
two  main  purposes :  it  is  an  aid  in  the  selection  of  food  and  it 
is  a  means  of  stimulating  the  digestive,  glands  (page  161). 

The  Sensation  of  Smell.  —  The  sense  organs  of  smell 
are  found  in  the  mucous  membrane  lining  the  upper  divi- 
sions of  the  nasal  cavities.  Here  are  found  two  kinds  of 


4 


Olfactory 
bulb 


A  B 

FIG.  147.  —  Sense  organ  of  smell.  A.  Distribution  of  nerves  in  outer 
wall  of  nasal  cavity.  I.  Turbinated  bones.  2.  Branch  of  fifth  pair  of  nerves. 
3.  Branches  of  olfactory  nerve.  4.  Olfactory  bulb.  B.  Diagram  showing 
connection  of  neurons  concerned  in  smell. 

cells  in  great  abundance  —  column-shaped  epithelial  cells 
and  the  cells  which  are  recognized  as  the  sense  organs  of 
smell.  These  olfactory  cells  are  spindle-shaped,  having  at 
one  end  a  slender,  thread-like  projection  which  reaches 
the  surface,  and  at  the  other  end  a  fiber  which  joins  an 
olfactory  nerve  (B,  Fig.  147).  In  fact,  the  olfactory  cells 


PRODUCTION   OF   SENSATIONS  347 

resemble  closely  the  cell-bodies  of  neurons,  and  are  thought 
to  be  such.  The  divisions  of  the  olfactory  nerve  pass 
through  many  small  openings  in  the  ethmoid  bone  to 
connect  with  the  olfactory  bulbs,  which  in  turn  connect 
with  the  cerebrum  (A,  Fig.  147). 

The  Olfactory  Stimulus.  —  Only  substances  in  the  gas- 
eous state  can  be  smelled.  From  this  it  is  inferred  that  the 
stimulus  is  supplied  by  gas  particles.  Solids  and  liquids  are 
smelled  because  of  the  gas  particles  which  separate  from 
them.  The  substance  which  is  smelled  must  be  kept  mov- 
ing through  the  nostrils  and  made  to  come  in  direct  contact 
with  the  olfactory  cells.  There  is  practically  no  limit  to 
the  number  of  distinct  odors  that  may  be  recognized. 

Value  of  Smell.  —  Although  the  sense  of  smell  is  not  so 
acute  in  man  as  in  some  of  the  lower  animals,  it  is,  never- 
theless, a  most  important  and  useful  gift.  It  is  the  only 
sense  that  responds  to  matter  in  the  gaseous  state,  and  is, 
for  this  reason,  the  only  natural  means  of  detecting  harm- 
ful constituents  of  the  atmosphere.  In  this  connection  it 
has  been  likened  to  a  sentinel  standing  guard  over  the  air 
passages.  Many  gases  are,  however,  without  odor,  and 
for  this  reason  cannot  be  detected  by  the  nostrils.  It  is  of 
especial  importance  that  gases  which  are  likely  to  become 
mixed  with  the  air  supply  to  the  body  have  odor,  even 
though  the  odor  be  disagreeable.  '  The  bad  odors  of 
illuminating  gas  and  of  various  compounds  of  the  chemical 
laboratory,  since  they  serve  as  danger  signals  to  put  one 
exposed  to  them  on  his  guard,  are  of  great  protective  value. 

Sight  and  Hearing.  —  The  sense  organs  of  sight  and 
hearing  are  highly  complicated  structures,  and  will  be 
considered  in  the  chapters  following. 

Summary.  —  Sensations  are  certain  activities  of  the 
mind  that  result  from  excitations  within  the  body  or  at  its 


348  COORDINATION   AND   SENSATION 

surface.  These  cause  the  neurons  to  discharge  impulses 
which  on  reaching  the  cerebrum  cause  the  sjensations. 
Sensations  are  necessary  for  intelligent  and  purposeful 
action  and  for  acquiring  all  kinds  of  knowledge.  To 
enable  the  stimuli  to  act  to  the  best  advantage  in  starting 
the  impulses,  special  devices,  called  sense  organs,  are 
employed.  These  receive  the  terminations  of  the  neurons, 
and  by  their  special  structure  enable  the  most  delicate 
stimuli  to  start  impulses.  The  simpler  forms  of  sense 
organs  are  those  of  touch,  temperature,  taste,  and  smell. 

Exercises. —  I.  Compare-sensations  and  reflex  actions  with  reference 
to  their  nature  and  cause.  Give  steps  in  the  production  of  each. 

2.  Give  examples  of  sensation  stimuli.     State  the  purpose  of  sense 
organs. 

3.  How  do  general  sensations  differ  from  special  sensations? 

4.  Of  what  value  is  pain  in  the  protection  of  the  body? 

5.  Show  that  sensations  lead  to  the  higher  forms  of  mental  activity, 
such  as  emotion  and  imagination. 

6.  Of  what  value  to  the  body  is  the  "  localizing  of  the  sensation  "  ? 

7.  What  kinds  of  sense  organs  are  found  in  the  skin?     State  the 
purpose  of  each. 

8.  Through  what  sense  avenues   is  one   made  aware  of  solids,  of 
liquids,  and  of  gases  ? 

9.  Of  what  special  protective  value  is  the  sense  of  smell  ? 

PRACTICAL   WORK 

To  demonstrate  the  Pacinian  Corpuscles.  —  Spread  out  the  mesen- 
tery from  the  intestine  of  a  cat  and  hold  it  between  the  eye  and  the 
light.  Pacinian  corpuscles  will  appear  as  small  translucent  bodies  hav- 
ing the  general  form  of  grains  of  wheat.  Secure  a  portion  of  the  mesen- 
tery over  a  circular  opening  in  a  thin  piece  of  cork  and  examine  it  with 
a  microscope  of  low  power.  Follow  the  course  of  the  nerve  fiber  to  the 
nerve  from  which  it  branches. 

To  show  Relative  Sensitiveness  of  Different  Parts  of  the  Skin. — 
Holding  a  bristle  between  the  fingers,  bring  the  end  in  contact  with  the 
skin,  noting  the  amount  of  pressure  necessary  to  cause  a  sensation  of 


PRODUCTION  OF   SENSATIONS  349 

touch.  Test  the  lips,  tongue,  tips  of  fingers,  and  palm  and  back  of 
hand,  trying  different  sizes  of  bristles.  Has  the  degree  of  sensitiveness 
any  relation  to  the  thickness  of  the  cuticle  ? 

To  show  Perceptive  Differences  of  Different  Portions  of  the  Skin.  — 
Place  the  points  of  a  pair  of  dividers  on  the  back  of  the  hand  of  one 
who  looks  in  the  opposite  direction.  Is  one  point  felt  or  two  ?  Repeat 
several  times,  changing  the  distance  between  the  points  until  it  is  fully 
determined  how  near  the  two  points  must  be  placed  in  order  to  be  felt 
as  one.  In  like  manner  test  other  parts  of  the  body,  as  the  tips  of  the 
fingers  and  the  back  of  the  neck.  Compare  results  obtained  at  differ- 
ent places. 

To  locate  Warm  and  Cold  Sensation  Spots.  —  Slowly  and  evenly 
draw  a  blunt-pointed  piece  of  metal  over  the  back  of  the  neck.  If  it  be 
of  the  same  temperature  as  the  skin,  only  touch  sensations  will  be  expe- 
rienced. If  it  be  a  little  colder  (the  temperature  of  the  room)  sensations 
of  cold  will  be  felt  at  certain  spots.  If  slightly  warmer  than  the  body, 
heat  sensation  spots  will  be  found  on  other  parts  of  the  skin.  If  the 
heat  and  cold  sensation  spots  be  marked  and  tested  from  day  to  day 
they  will  be  found  to  remain  constant  as  to  position.  Inference. 


CHAPTER   XXI 
THE  LARYNX  AND  THE  EAR 

MAN  is  a  social  being.  His  inclinations  are  not  to  live 
alone,  but  to  be  a  part  of  that  great  human  organization 
known  as  society.  For  men  to  work  together,  to  be  mutu- 
ally helpful  one  to  another,  requires  the  ability  to  exchange 
ideas  and  this  in  turn  requires  some  means  of  communica- 
tion.1 One  meang  of  communication  is  found  in  certain 
movements  of  the  atmosphere,  known  as  sound  waves. 
In  the  exchange  of  ideas  by  this  means  there  are  employed 
two  of  the  most  interesting  divisions  of  the  body  —  the 
larynx  and  the  ear.  The  first  is  an  instrument  for  the 
production  of  sound  waves ;  the  second  is  th^.  sense  organ 
which  enables  the  sound  waves  to  act  as  stimuli  to  the 
nervous  system. 

Nature  of  Sound  Waves.  —  If  some  sonorous  body,  as  a 
bell,  be  struck,  it  is  given  a  quivering,  or  vibratory,  motion. 
This  is  not  confined  to  the  bell,  but  is  imparted  to  the  air 
and  other  substances  with  which  the  bell  comes  in  contact. 
These  take  up  the  movements  and  pass  them  to  objects 
more  remote,  and  they  in  turn  give  them  to  others,  until  a 
very  considerable  distance  is  reached.  Such  progressive 
vibrations  are  known  as  waves,  and,  since  they  act  as 
stimuli  to  the  organs  of  hearing,  they  are  called  sound 
waves.  Sound  waves  always  originate  in  vibrating  bodies? 

1  The  problem  of  social  adjustment  is  but  a  phase  of  the  general  problem  of 
establishing  proper  relations  between  the  body  and  its  surroundings. 

2  A  vibrating  body  is  one  having  a  to-and-fro  movement,  like  that  of  a  clock 
pendulum  or  the  string  of  a  violin  on  sounding.     Bodies  to  give  out  sourtd  waves 

35° 


THE   LARYNX   AND   THE   EAR  35! 

They  are  transmitted  chiefly  by  the  air,  which,  because  of 
its  lightness,  elasticity,  and  abundance,  readily  takes  up  the 
vibrations  and  spreads  them  in  all  directions  (Fig.  148). 

While  these  vibratory  movements  of  the  atmosphere  are  correctly 
classified  as  waves,  they  bear  little  resemblance  to  the  waves  on  water. 
Instead  of  being  made  of  crests  and  troughs,  as  are  the  water  waves, 


FIG.  148.  —  Diagram  illustrating  the  spreading  of  sound 
waves  through  air. 

the  sound  waves  consist  of  alternating  successions  of  slightly  condensed 
and  rarefied  layers  of  air.  Then,  while  the  general  movement  of  the 
water  waves  is  that  of  ever  widening  circles  over  a  surface,  the  sound 
waves  spread  as  enlarging  spherical  shells  through  the  air.  In  sound 
waves,  as  in  all  other  waves,  however,  it  is  only  the  form  of  the  wave 
that  moves  forward.  The  individual  particles  of  air  that  make  up  the 
wave  simply  vibrate  back  and  forth. 

How  Sound  Waves  act  as  Stimuli.  —  Any  sound  wave 
represents  a  small  but  definite  amount  of  energy,  this 
being  a  part  of  the  original  force  that  acted  on  the  vibrating 
body  to  set  it  in  motion.  The  hammer,  for  instance,  in 
striking  a  bell  imparts  to  it  a  measurable  quantity  of 
energy,  which  the  bell  in  turn  imparts  to  the  air.  This 
energy  is  in  the  sound  waves  and  is  communicated  to  the 

must  vibrate  rapidly,  making  not  less  than  sixteen  vibrations  per  second.  The 
upper  limit  of  hearing  being  about  40,000  vibrations  per  second,  certain  bodies 
may  even  vibrate  too  rapidly  to  be  heard. 


352  COORDINATION    AND    SENSATION 

bodies  against  which  they  strike.1  Though  the  force  exerted 
by  most  sound  waves  is,  indeed,  very  slight,  it  is  sufficient 
to  enable  them  to  act  as  stimuli  to  the  nervous  system. 

How  Sounds  Differ.  —  Three  distinct  effects  are  produced  by  sound 
waves  upon  the  nerves  of  hearing,  and  through  them  upon  the  mind. 
These  are  known  as  pitch,  intensity,  and  quality,  and  they  are  depend- 
ent upon  the  vibrations  of  the  sound-producing  bodies. 

Pitch,  which  has  reference  to  the  height,  or  degree  of  sharpness,  of 
tones,  is  determined  by  the  rapidity  of  the  vibrations  of  the  vibrating 
body.  The  more  rapid  the  vibrations,  the  higher  the  pitch,  the 
number  of  vibrations  doubling  for  each  musical  interval  known  as 
the  octave. 

Intensity  is  the  energy,  or  force,  of  the  sound  waves.  This  is  recog- 
nized by  the  strength  of  the  sensation  and  is  expressed  by  the  term 
loudness.  Intensity  is  governed  mainly  by  the  width  of  the  vibrations 
of  the  vibrating  body,  and  the  width  depends  upon  the  force  applied 
to  the  body  to  make  it  vibrate. 

Quality  is  that  peculiarity  of  sound  that  enables  tones  from  different 
instruments  to  sound  differently,  although  they  may  have  the  same 
pitch  and  intensity.  Quality  depends  upon  the  fact  that  most  tones  are 
complex  in  nature  and  result  from  the  blending  together  of  simple  tones 
of  different  pitch. 

Reinforcement  of  Sound  Waves.  —  The  sound  vibrations  from 
small  bodies  are  not  infrequently  reenforced  by  surrounding  conditions 
so  that  their  outgoing  waves  reach  farther  and  are  more  effective  than 
waves  from  larger  bodies.  This  is  true  of  the  sound  waves  produced 
by  most  musical  instruments  and  also  those  produced  by  the  human 
larynx.  Such  reinforcement  is  effected  in  two  general  ways  —  by 
sounding  boards  and  by  inclosed  columns  of  air.  Stringed  instru- 
ments —  violin,  guitar,  piano,  etc.  —  employ  sounding  boards,  while 
wind  instruments,  as  the  flute,  pipe  organ,  and  the  various  kinds  of 
horns,  employ  air  columns  for  reenforcing  their  vibrations.  In  the  use 
of  the  sounding  board,  the  vibrations  are  communicated  to  a  larger  sur- 
face, and  in  the  use  of  the  air  column  the  vibrations  are  communi- 
cated to  the  inclosed  air.  (See  Practical  Work.) 

1  Somewhat  as  the  waves  on  a  body  of  water  impart  motion  to  the  sticks  and 
weeds  along  the  shore,  sound  waves  are  able  to  cause  bodies  that  are  small  or  that 
are  delicately  poised  to  vibrate. 


THE  LARYNX  AND  THE  EAR         353 

Value  of  Sound  Waves  to  the  Body.  —  From  a  physio- 
logical standpoint,  the  value  of  sound  waves  is  not  easily 
overestimated.  In  addition  to  the  use  made  of  them  in 
the  communication  of  ideas,  they  serve  the  purpose  of 
protecting  the  body,  and  in  the  sphere  of  music  provide 
one  of  the  most  elevating  forms  of  entertainment.  Sounds 
from  different  animals,  as  well  as  from  inanimate  objects, 
may  also  be  the  means  of  supplying  needed  information. 
The  existence  of  two  kinds  of  sound  instruments  in  the 
body  —  the  one  for  the  production,  the  other  for  the  detec- 
tion, of  sound  —  is  certainly  suggestive  of  the  ability  of  the 
body  to  adjust  itself  to,  and  to  make  use  of,  its  physical  en- 
vironment. Both  the  larynx  and  the  ear  are  constructed 
with  special  reference  to  the  nature  and  properties  of  sound 
waves. 

THE    LARYNX 

The  Sound-producing  Mechanism  of  the  Body  consists  of 
the  following  parts  : 

1.  Delicately  arranged   bodies   that   are  easily   set   in 
vibration. 

2.  An  arrangement  for  supplying  the  necessary  force 
for  making  these  bodies  vibrate. 

3.  Contrivances  for  modifying  the  vibrating  parts  so  as 
to  produce  changes  in  pitch  and  intensity. 

4.  Parts  that  reenforce  the  vibrations. 

5.  Organs  by  means  of  which  the  sounds  are  converted 
into  the  forms  of  speech. 

The  central  organ  in  this  complex  mechanism  is 

The  Larynx.  —  The   larynx   forms   a   part   of   the   air 

passages,  being  a  short  tube   at   the  upper  end  of   the 

trachea.     Mucous  membrane    lines   the  inside  of   it  and 

muscles  cover  most  of  the  outer  surface.     The  framework 


354 


COORDINATION   AND   SENSATION 


is  made  of  cartilage.  At  the  top  it  is  partly  encircled  by 
a  small  bone  (the  hyoid),  and  its  opening  into  the  pharynx 
is  guarded  by  a  flexible  lid,  called  the  epiglottis.  The 
cartilage  in  its  walls  is  in  eight  separate  pieces,  but  the 
greater  portion  of  the  structure  is  formed  of  two  pieces 
only.  These  are  known  as  the  thyroid  cartilage  and  the 
cricoid  cartilage  (Fig.  149).  Both  can  be  felt  in  the  throat 
—  the  thyroid  as  the  projection  known  as  "Adam's  apple," 
and  the  cricoid  as  a  broad  ring  just  below. 

The  thyroid  cartilage  consists  of  two  V-shaped  pieces, 
one  on  either  side  of  the  larynx,  meeting  at  their  points 


A  B 

FIG.  149. — The  larynx.  —  A.  Outside  view.  B.  Vertical  section 
through  larynx,  showing  inside.  I.  Thyroid  cartilage.  2.  Cricojd  carti- 
lage. 3.  Trachea.  4.  Hyoid  bone.  5.  Epiglottis.  6.  Vocal  cord. 
7.  False  vocal  cord.  8.  Lining  of  mucous  membrane. 

in  front,  and  each  terminating  at  the  back  in  an  upward 
and  a  downward  projection.  Between  the  back  portions 
of  the  thyroid  is  a  space  equal  to  about  one  third  of  the 
circumference  of  the  larynx.  This  is  occupied  by  the 
greater  portion  of  the  cricoid  cartilage.  This  cartilage 


THE   LARYNX   AND   THE  EAR 


355 


has  the  general  shape  of  a  signet  ring  and  is  so  placed 
that  the  part  corresponding  to  the  signet  fits  into  the  thy- 
roid space,  while  the  ring  portion  encircles  the  larynx  just 
below  the  thyroid.  Muscles  and  connective  tissue  pass 
from  the  thyroid  to  the  cricoid  cartilage  at  all  places,  save 
one  on  each  side,  where  the  downward  projections  of  the 
thyroid  form  hinge  joints  with  the  cricoid.  These  joints 
permit  of  motion  of  either  cartilage  upon  the  other. 

At  the  summit  of  the  cricoid  cartilage,  on  each  side,  is 
a  small  piece  of  triangular  shape,  called  the  arytenoid 
cartilage.  Each  arytenoid  is  movable  on  the  cricoid  and 
is  connected  with  one  end  of  a  vocal  cord. 

The  Vocal  Cords  are  formed  by  two  narrow  strips  of 
tissue  which,  connecting  with  the  thyroid  cartilage  in  front 
and  the  arytenoid  cartilages  behind,  lie  in  folds  of  the 
mucous  membrane.  They  have  the  general  appearance 
of  ridge-like  projections  from  the  sides  of  the  larynx,  but 


—         Epiglottis 
False  Vocal  Cords 

True  Vocal  Cords 


A 

FlG.  150.  —Vocal  cords  as  seen  from  above.     A.  In  producing  sound. 
£.  During  quiet  breathing. 

at  their  edges  they  are  sharp  and  smooth.  The  open  space 
between  the  cords  is  called  the  glottis.  When  sound  is 
not  being  produced,  the  glottis  is  open  and  has  a  triangular 
form,  due  to  the  spreading  apart  of  the  arytenoid  cartilages 
and  the  attached  cords.  But  when  sound  is  being  pro- 
duced, the  glottis  is  almost  completely  closed  by  the  cords. 
Above  the  vocal  cords,  and  resembling  them  in  appear- 


356  COORDINATION   AND   SENSATION 

ance,  are  two  other  folds  of  membrane,  called  the  false 
vocal  cords  (B,  Fig.  149).  The  false  cords  do  not  produce 
sound,  but  they  aid  in  the  closing  of  the  glottis. 

How  the  Voice  is  Produced.  —  The  voice  is  produced 
through  the  vibrations  of  the  vocal  cords.  A  special  set 
of  muscles  draws  the  arytenoid  cartilages  toward  each 
other,  thereby  bringing  their  edges  very  near  and  parallel 
to  each  other  in  the  passage.  At  the  same  time  other 
muscles  act  on  the  thyroid  and  cricoid  cartilages  to  separate 
them  at  the  top  and  give  the  cords  the  necessary  tension. 
With  the  glottis  now  almost  closed,  blasts  of  air  from  the 
lungs  strike  the  sharp  edges  of  the  cords  and  set  them  in 
vibration  (Fig.  150).  The  vocal  cords  do  not  vibrate  as 
strings,  like  the  strings  of  a  violin,  but  somewhat  as  reeds, 
similar  to  the  reeds  of  a  French  harp  or  reed  organ. 

The  location  of  the  vocal  cords  in  the  air  passages  enables 
the  lungs  and  the  muscles  of  respiration  to  aid  in  the  pro- 
duction of  the  voice.  It  is  their  function  to  supply  the 
necessary  force  for  setting  the  cords  in  vibration.  The 
upper  air  passages  (mouth,  nostrils,  and  pharynx)  supply 
resonance  chambers  for  reenforcing  the  vibrations  from 
the  vocal  cords,  thereby  greatly  increasing  their  intensity. 
In  ordinary  breathing  the  vocal  cords  are  in  a  relaxed  con- 
dition against  the  sides  of  the  larynx  and  are  not  acted 
upon  by  the  air  as  it  enters  or  leaves  the  lungs. 

Pitch  and  Intensity  of  the  Voice.  —  Changes  in  the  pitch 
of  the  voice  are  caused  mainly  by  variations  in  the  tension 
of  the  cords,  due  to  the  movements  of  the  thyroid  and 
cricoid  cartilages  upon  each  other.1  In  the  production  of 
tones  of  very  high  pitch,  the  vibrating  portions  of  the  cords 

1  Some  idea  of  how  the  movements  of  the  cartilages  change  the  tension  of  the 
cords  may  be  obtained  by  holding  the  fingers  on  the  larynx,  between  the  thyroid 
and  cricoid  cartilages,  and  making  tones  first  of  low  and  then  of  high  pitch.  For 


THE   LARYNX   AND   THE   EAR  357 

are  thought  to  be  actually  shortened  by  their  margins  being 
drawn  into  contact  at  the  back.  This  raises  the  pitch  in 
the  same  manner  as  does  the  shortening  of  the  vibrating 
portion  of  a  violin  string. 

The  intensity,  or  loudness,  of  the  voice  is  governed 
by  the  force  with  which  the  air  is  expelled  from  the 
lungs.  The  vibrations  of  the  cords,  however,  are  greatly 
reenforced  by  the  peculiar  structure  of  the  upper  air  pas- 
sages, as  stated  above. 

Production  of  Speech.  —  The  sounds  that  form  our  speech 
or  language  are  produced  by  modifying  the  vibrations  from 
the  vocal  cords.  This  is  accomplished  by  "mouthing"  the 
sounds  from  the  larynx.  The  distinct  sounds,  or  words, 
are  usually  complex  in  nature,  being  made  up  of  two  or 
more  elementary  sounds.  These  are  classed  either  as 
vowels  or  consonants  and  are  represented  by  the  different 
letters  of  the  alphabet.  The  vowel  sounds  are  made  with 
the  mouth  open  and  are  more  nearly  the  pure  vibrations  of 
the  vocal  cords.  The  consonants  are  modifications  of  the 
vocal  cord  vibrations  produced  by  the  tongue,  teeth,  lips, 
and  throat. 

Words  and  their  Significance.  —  In  the  development  of 
language  certain  ideas  have  become  associated  with  cer- 
tain sounds  so  that  the  hearing  of  these  sounds  suggests 
the  ideas.  Our  words,  therefore,  consist  of  so  many  sound 
signals,  each  capable  of  arousing  a  definite  idea  in  the 
mind.  To  talk  is  to  express  ideas  through  these  signals, 
and  to  listen  is  to  assume  an  attitude  of  mind  such  that  the 
signals  may  be  interpreted.  In  learning  a  language,  both 
the  sounds  of  the  words  and  their  associated  ideas  are 

the  high  tones  the  cartilages  are  pulled  together  in  front,  and  for  the  low  tones  they 
separate.  As  they  pull  together  in  front,  they  of  course  separate  behind  and  above, 
where  the  cords  are  attached. 


358  COORDINATION    AND    SENSATION 

mastered,  this  being  necessary  to  their  practical  use  in 
exchanging  ideas.  From  spoken  language  man  has  ad- 
vanced to  written  language,  so  that  the  sight  of  the  written 
or  printed  word  also  arouses  in  the  mind  the  associated 
idea. 

THE  EAR 

The  Ear  is  the  sense  organ  which  enables  sound  waves 
to  so  act  upon  afferent  neurons  as  to  excite  impulses  in 
them.  The  effect  upon  the  mind  which  these  impulses 
produce  is  known  as  the  sensation  of  hearing.  In  the 
performance  of  its  function  the  ear  receives  and  transmits 
sound  waves  and  also  concentrates  them  upon  a  suitable 
exposure  of  nerve  cells.  It  includes  three  parts  —  the 
external  ear,  the  middle  ear,  and  the  internal  ear. 

External  Ear.  —  The  external  ear  consists  of  the  part 
on  the  outside  of  the  head  called  the  pinna,  or  auricle,  and 
the  tube  leading  into  the  middle  ear,  called  the  auditory 
canal  (Fig.  151).  The  pinna  by  its  peculiar  shape  aids  to 
some  extent  the  entrance  of  sound  waves  into  the  auditory 
canal.1  It  consists  chiefly  of  cartilage.  The  auditory  canal 
is  a  little  more  than  an  inch  in  length  and  one  fourth  of  an 
inch  in  diameter,  and  is  closed  at  its  inner  end  by  a  thin, 
but  important  membrane,  called 

The  Membrana  Tympani.  —  This  membrane  consists  of 
three  thin  layers.  The  outer  layer  is  continuous  with  the 
lining  of  the  auditory  canal ;  the  inner  is  a  part  of  the  lin- 
ing of  the  middle  ear ;  and  the  middle  is  a  fine  layer  of 
connective  tissue.  Being  thin  and  delicately  poised,  the 
membrana  tympani  is  easily  made  to  vibrate  by  the  sound 

1  It  is  only  the  central  portion  of  the  pinna  that  aids  the  entrance  of  sound  into 
the  auditory  canal.  If  by  accident  the  outer  portion  of  the  pinna  is  removed,  there 
is  no  impairment  of  the  hearing. 


THE   LARYNX   AND   THE    EAR 


359 


waves  that  enter  the  auditory  canal.  In  this  way  it  serves 
as  a  receiver  of  sound  waves  from  the  air.  It  also  protects 
The  Middle  Ear.  —The  middle  ear,  or  tympanum,1  con- 
sists of  an  irregular  cavity  in  the  temporal  bone  which  is 
lined  with  mucous  membrane  and  filled  with  air.  It  is 


Coch/es 


Evstachian 
tube 


FIG.  151.  — Diagram  of  section  through  the  ear,  showing  relations 
of  its  various  parts.     (See  text.) 

connected  with  the  pharynx  by  a  slender  canal  called  the 
Eustachian  tube.  Extending  across  the  middle  ear  and 
connecting  with  the  membrana  tympani  on  one  side,  and 
with  a  membrane  closing  a  small  passage  to  the  internal 
ear  on  the  other,  is  a  tiny  bridge  formed  of  three  small 
bones.  These  bones,  named  in  their  order  from  the  mem- 
brana tympani,  are  the  malleus,  the  incus,  and  the  stapes 
(Fig.  151).  Where  the  malleus  joins  the  membrane  is  a 
small  muscle  whose  contraction  has  the  effect  of  tighten- 

1  The  middle  ear  is  also  called  the  ear  drum,  and,  by  the  same  system  of  nam- 
ing, the  membrana  tympani  is  referred  to  as  the  drum  membrane. 


360  COORDINATION   AND   SENSATION 

ing  the  membrane.  The  Eustachian  tube  admits  air 
freely  to  the  middle  ear,  providing  in  this  way  for  an  equal- 
ity of  atmospheric  pressure  on  the  two  sides  of  the  drum 
membrane.  The  bridge  of  bones  and  the  air  in  the 
middle  ear  receive  vibrations  from  the  membrana  tympani 
and  communicate  them  to  the  membrane  of  the  internal  ear. 

Purposes  of  the  Middle  Ear.  —  The  middle  ear  serves  two  important 
purposes.  In  the  first  place,  it  makes  it  possible  for  sound  waves  to 
set  the  membrana  tympani  in  vibration.  This  membrane  could  not 
be  made  to  vibrate  by  the  more  delicate  of  the  sound  waves  if  it  were 
stretched  over  a  bone,  or  over  some  of  the  softer  tissues,  or  over  a  liquid. 
Its  vibration  is  made  possible  by  the  presence  of  air  on  both  sides, 
and  this  condition  is  supplied,  on  the  inner  side,  by  the  middle  ear. 
The  Eustachian  tube,  by  providing  for  an  equality  of  pressure  on  the 
two  sides  of  the  membrane,  also  aids  in  this  purpose. 

In  the  second  place,  the  middle  ear  provides  a  means  for  concentrat- 
ing the  force  of  the  sound  waves  as  they  pass  from  the  membrana 
tympani  to  the  internal  ear.  This  concentration  is  effected  in  the  fol- 
lowing manner : 

1.  The  bridge  of  bones,  being  pivoted  at  one  point  to  the  walls  of 
the  middle  ear,  forms  a  lever  in  which  the  malleus  is  the  long  arm,  and 
the  incus  and  stapes  the  short  arm,  their  ratio  being  about  that  of  three 
to  two.     This  causes  the  incus  to  move  through  a  shorter  distance,  but 
with  greater  force  than  the  end  of  the  malleus. 

2.  The  area  of  the  membrana  tympani  is  about  twenty  times  as  great 
as  the  membrane  of  the  internal  ear  which  is  acted  upon  by  the  stapes. 
The  force  from  the  larger  surface  is,  therefore,  concentrated  by  the 
bridge  of  bones  upon  the  smaller  surface.     By  the  combination  of  these 
two  devices,  the  waves  striking  upon  the  membrane  of  the  internal  ear 
are  rendered  some  thirty  times  more  effective  than  are  the  same  waves 
entering  the  auditory  canal. 

The  Internal  Ear,  or  labyrinth,  occupies  a  series  of  ir- 
regular channels  in  the  petrous  process  of  the  temporal 
bone.1  It  is  very  complicated  in  structure,  and  at  the 
same  time  is  very  small.  Its  greatest  length  is  not  more 

1  The  inner  projection  of  the  temporal  bone  is  known  as  the  petrous  process. 


THE   LARYNX   AND   THE   EAR 


361 


than  three  fourths  of  an  inch  and  its  greatest  diameter  not 
more  than  one  half  of  an  inch.  It  is  filled  with  a  liquid 
which  at  one  place  is  called  the  perilymph,  and  at  another 
place  the  endolymph.  It  is  a  double  organ,  being  made  up 
of  an  outer  portion  which  Ues  next  to  the  bone,  and  which 
surrounds  an  inner  portion  of  the  same  general  form. 
The  outer  portion  is  surrounded  by  a  membrane  which 
serves  as  periosteum  to 
the  bone  and,  at  the 
same  time,  holds  the 
liquid  belonging  to  this 
part,  called  the  peri- 
lymph.  The  inner 
portion,  called  the  mem- 
branous labyrinth,  con- 
sists essentially  of  a 
closed  membranous  sac, 
which  is  filled  with  the 
endolymph.  The  audi- 
tory nerve  terminates 


FIG.    152.  —  General  form  of   internal 
ear.     The  illustration  represents  the  struc- 
in    this    portion    of    the    tures  of  the  internal  ear  surrounded  by  a 

internal     ear.       Three  thin  laygr  of  bone'    '•  Vestibule-    2-  Coch' 

lea.     3 

ovalis. 


Semicircular   canals. 
Fenestra  rotunda. 


4.    Fenestra 


distinct  divisions  of  the 

labyrinth      have     been 

made  out,  known  as  the  vestibule,  the  semicircular  canals, 

and  the  cochlea  (Fig.  152). 

The  Vestibule  forms  the  central  portion  of  the  internal 
ear  and  is  somewhat  oval  in  shape.  It  is  in  communication 
with  the  middle  ear  through  a  small  opening  in  the  bone, 
called  fazfenestra  ovalis,  at  which  place  it  is  separated 
from  the  middle  ear  only  by  a  thin  membrane.  Sound 
waves  enter  the  liquids  of  the  internal  ear  at  this  point, 
the  foot  of  the  stapes  being  attached  to  the  membrane. 


362  COORDINATION   AND    SENSATION 

Six  other  openings  lead  off  from  the  vestibule  at  different 
places.  One  of  these  enters  the  cochlea.  The  other  five 
open  into 

The  Semicircular  Canals.  —  These  canals,  three  in  num- 
ber, pass  through  the  bone  in  three  different  planes.  One 
extends  in  a  horizontal  direction  and  the  other  two  verti- 
cally, but  each  plane  is  at  right  angles  to  the  other  two. 
Both  ends  of  each  canal  connect  with  the  vestibule,  though 
two  of  them  join  by  a  common  opening.  The  inner  mem- 
branous labyrinth  is  continuous  through  each  canal,  and 
is  held  in  position  by  small  strips  of  connective  tissue. 

The  purpose  of  the  semicircular  canals  is  not  under- 
stood. It  is  known,  however,  that  they  are  not  used  in 
hearing.  On  the  other  hand,  there  is  evidence  to  the 
effect  that  they  act  as  equilibrium  sense  organs,  exciting 
sensations  necessary  for  balancing  the  body.  Their  re- 
moval or  injury,  while  having  no  effect  upon  the  hear- 
ing, does  interfere  with  the  ability  to  keep  the  body  in  an 
upright  position. 

The  Cochlea  is  the  part  of  the  internal  ear  directly  con- 
cerned in  hearing.    It  consists  of  a  coiled  tube  which  makes 
two  and   one   half   turns   around   a 
central  axis  and  bears  a  close  resem- 
blance  to  a  snail  shell  (Figs.  151  and 
152).     It  differs  in  plan  from  a  snail 
shell,    however,  in  that   its   interior 
space   is  divided  into  three  distinct 
l?'    I,53'  T  .  iagram   channels,  or  canals.     These  lie  side 

showing    the    divisions    of 

cochlear  canal.  bY  Slde  and  are  named,  from  their 

relations   to  other    parts,   the   scala 

vestibula,-'ChQ.  scala  tympani,  and  the  scala.  media.  Any 
vertical  section  of  the  cochlea  shows  all  three  of  these 
channels  (Fig.  153). 


THE    LARYNX   AND   THE   EAR  363 

The  Scala  Vestibula  and  the  Scala  Tympani  appear  in 
cross  section  as  the  larger  of  the  canals.  The  formert 
,so  named  from  its  connection  with  the  vestibule,  occupies 
the  upper  position  in  all  parts  of  the  coil.  The  latter  lies 
below  at  all  places,  and  is  separated  from  the  channels 
above  partly  by  a  margin  of  bone  and  partly  by  a  mem- 
brane. It  receives  its  name  from  its  termination  at  the 
tympanum,  or  middle  ear,  from  which  it  is  separated  only 
by  a  thin  membrane.1  Both  the  scala  vestibula  and  the 
scala  tympani  belong  to  the  outer  portion  of  the  internal 
ear  and  are,  for  this  reason,  filled  with  the  perilymph.  At 
their  upper  ends  they  communicate  with  each  other  by  a 
small  opening,  making  by  this  means  one  continuous  canal 
through  the  cochlea.  This  canal  passes  from  the  vesti- 
bule to  the  tympanum  and,  in  so  doing,  goes  entirely 
around 

The  Scala  Media.  —  This  division  of  the  cochlea  lies 
parallel  to  and  between  the  other  two  divisions.  It  is 
above  the  scala  tympani  and  below  the  scala  vestibula, 
and  is  separated  from  each  by  a  membrane.  The  scala 
media  belongs  to  the  membranous  portion  of  the  internal 
ear  and  is,  therefore,  filled  with  the  endolymph.  It  receives 
the  terminations  of  fibers  from  the  auditory  nerve  and  may 
be  regarded  as  the  true  sense  organ  of  hearing.  The  nerve 
fibers  terminate  upon  the  membrane  known  as  the  basilar 
membrane,  which  separates  it  from  the  scala  tympani. 
This  membrane  extends  the  length  of  the  cochlear  canals, 
and  is  stretched  between  a  projecting  shelf  of  bone  on  one 
side  and  the  outer  wall  of  the  cochlea  on  the  other.  It  is 
covered  with  a  layer  of  epithelial  cells,  some  of  which  have 
small,  hair-like  projections  and  are  known  as  the  hair  cells. 
Above  the  membrane,  and  resting  partly  upon  it,  are  two 

i  A  small  opening  in  the  bone  at  this  place  is  called  \\iefenestra  rotunda. 


364 


COORDINATION   AND   SENSATION 


rows  of  rod-like  bodies,  called  the  rods  of  Corti.  These, 
by  leaning  toward  each  other,  form  a  kind  of  tunnel  be- 
neath. They  are  exceedingly  numerous,  numbering  more 
than  6000,  and  form  a  continuous  series  along  the  margin 
of  the  membrane. 

How  We  Hear.  —  The  sound  waves  which  originate  in 
vibrating  bodies  are  transmitted  by  the  air  to  the  external 
ear.  Passing  through  the  auditory  canal,  the  waves  strike 

against  the  membrana 
tympani,  setting  it  into 
vibration.  By  the  bridge 
of  bones  and  the  air 
within  the  middle  ear 
the  vibrations  are  carried 
to  and  concentrated  upon 
the  liquid  in  the  internal 
ear  (Fig.  154).  From 
here  the  vibrations  pass 
through  the  channels  of 
the  cochlea  and  set  into  vibration  the  contents  of  the  scala 
media  and  different  portions  of  the  basilar  membrane. 
This  serves  as  a  stimulus  to  the  fibers  of  the  auditory 
nerve,  causing  them  to  transmit  impulses  which,  on  passing 
to  the  brain,  produce  the  sensation  of  hearing. 

Much  of  the  peculiar  structure  of  the  cochlea  is  not  understood.  Its 
minute  size  and  its  location  in  the  temporal  bone  make  its  study  extremely 
difficult.  The  connection  of  the  scala  vestibula  with  the  scala  tympani, 
and  this  with  the  middle  ear,  is  necessary  for  the  passage  of  vibrations 
through  the  internal  ear.  Its  liquids,  being  practically  incompressible 
and  surrounded  on  all  sides  by  bones,  could  not  otherwise  yield  to  the 
movements  of  the  stapes.  (See  Practical  Work.)  The  rods  of  Corti 
are  thought  to  act  as  dampers  on  the  basilar  membrane,  to  prevent 
the  continuance  of  vibrations  when  once  they  are  started. 

Detection  of  Pitch.  — The  method  of  detecting  tones  of  different  pitch 


FIG.  154.  —  Diagram  illustrating  pas- 
sage of  sound  waves  through  the  ear. 


THE   LARYNX  AND   THE   LAR  365 

is  not  understood.  Several  theories  have  been  advanced  with  reference 
to  its  explanation,  one  of  the  most  interesting  being  that  proposed  by 
Helmholtz.  This  theory  is  based  on  our  knowledge  of  sympathetic 
vibrations.  The  basilar  membrane,  while  continuous  throughout,  may 
be  regarded  as  made  up  of  many  separate  cords  of  different  lengths 
stretched  side  by  side.  A  tone  of  a  given  pitch  will  set  into  vibration 
only  certain  of  these  cords,  while  tones  of  different  pitch  will  set  others 
into  vibration. 

Another  theory  is  that  the  basilar  membrane  responds  to  all  kinds 
of  vibrations  and  the  analysis  of  sound  takes  place  in  the  brain. 

A  third  view  is  that  the  filaments  from  the  hair  cells,  rather  than  the 
basilar  membrane,  respond  to  the  vibrations  and  in  turn  stimulate  the 
terminations  of  the  nerve  fibers. 

Hygiene  of  the  Ear. — The  ear,  being  a  delicate  organ, 
is  frequently  injured  by  careless  or  rough  treatment.  The 
removal  of  the  ear  wax  by  the  insertion 
of  pointed  instruments  has  been  found 
to  interfere  with  the  natural  method  of 
discharge  and  to  irritate  the  membrane. 
It  should  never  be  practiced.  It  is  un- 
necessary in  the  healthy  ear  thus  to 
cleanse  the  auditory  canal,  as  the  wax  is  FIG.  155.— Diagram 
passed  by  a  natural  process  to  where  showing  how  wax  may 

.    ,  ,  ,    , ,       plug  the  auditory  canal 

it  is  easily  removed  by  a  damp  cloth.  ^n(f  cause  deafness. 
If   the   natural    process   is   obstructed, 
clean  warm  water  and  a  soft  linen  cloth  may  be  employed 
in  cleansing  the  canal,  without  likelihood  of  injury.    Clean 
warm  water   may  also   be   introduced   into   the   auditory 
canal  as  a  harmless  remedy  in  relieving  inflammation  of 
the  auditory  canal  and  of  the  middle  ear.     Children's  ears 
are  easily  injured,  and  it  goes  without  saying  that  they 
should  never  be  pulled  nor  boxed. 

It  frequently  happens  that  a  mass  of  wax  collects  in  the 
auditory  canal  and  closes  the  passage  so  completely  as  to 


366  COORDINATION   AND    SENSATION 

cause  deafness  (Fig.  155).  This  may  come  about  with- 
out pain  and  so  gradually  that  one  does  not  think  of  seek- 
ing medical  aid.  Such  masses  are  easily  removed  by  the 
physician,  the  hearing  being  then  restored.  Both  for 
painful  disturbances  of  the  ear  and  for  the  gradual  loss 
of  hearing,  the  physician  should  be  consulted. 

The  Hearing  of  School  Children.  —  School  children  not 
infrequently  have  defective  hearing  and  for  this  reason 
are  slow  to  learn.  The  hearing  is  easily  tested  with  a 
watch,  the  normal  ear  being  able  to  hear  the  watch  tick 
at  a  distance  of  at  least  two  feet.  Pupils  with  defective 
hearing  should,  of  course,  have  medical  attention,  and  in 
the  classroom  should  be  seated  where  they  can  hear  to 
the  best  advantage. 

Summary.  —  Sound  waves  constitute  the  external  stimuli 
for  the  sensation  of  hearing.  They  consist  of  progressive 
vibratory  movements  of  the  air  that  originate  in  vibrating 
bodies.  Through  the  larynx  and  the  ear,  sound  waves  are 
utilized  by  the  body  in  different  ways,  but  chiefly  as  a 
means  of  communication.  The  larynx  produces  sound 
waves  which  are  reenforced  and  modified  by  the  air  pas- 
sages. The  ear  supplies  suitable  conditions  for  the  action 
of  sound  waves  upon  nerve  cells.  Both  the  ear  and  the 
larynx  are  constructed  with  special  reference  to  the  nature 
and  properties  of  sound  waves,  and  they  illustrate  the  body's 
ability  to  adjust  itself  to,  and  to  make  use  of,  its  physical 
environment. 

Exercises.  —  I .  For  what  different  purposes  are  sound  waves  em- 
ployed in  the  body  ? 

2.  How  do   sound  waves   originate  ?     How  are  they  transmitted  ? 
How  do  they  differ  from  the  waves  on  water  ? 

3.  How  are  sound  waves  able  to  act  as  nerve  stimuli  ? 

4.  Describe   two    methods   of  reenforcing  sound  waves.      Which 
method  is  employed  in  the  body  ? 


THE   LARYNX   AND   THE   EAR  367 

5.  Name  all  the  parts  of  the  body  that  are  directly  or  indirectly 
concerned  in  the  production  of  sound. 

6.  Describe  the  larynx. 

7.  Describe  the  condition  of  the  vocal  cords  in  speaking  and  in 
ordinary  breathing. 

8.  How  are  sounds  differing  in  pitch  and  intensity  produced  by  the 
larynx  ? 

9.  How  is  the  sound  produced  by  the  vocal  cords  changed  into 
speech  ? 

10.  What  parts   of  the  ear  are  concerned  in  transmitting  sound 
waves  ? 

11.  Give  the  purposes  of  the  middle  ear. 

12.  Trace  a  sound  wave  from  a  bell  to  the  basilar  membrane,  and 
trace  the  impulse  that  it  causes  from  there  to  the  brain. 

13.  Give  the  purpose  of  the  Eustachian  tubes  ;  of  the  rods  of  Corti ; 
of  the  semicircular  canals. 

14.  Give  directions  for  the  proper  care  of  the  ear. 

PRACTICAL  WORK 

To  illustrate  the  Origin  of  Sound.  —  i.  Strike  a  bell  an  easy  blow 
and  hold  some  light  substance,  as  a  pith  ball  attached  to  a  thread, 
against  the  side,  noting  the  result.  2.  Sound  a  tuning  fork  by  striking 
it  against  the  table.  Test  it  for  vibrations  as  above,  or  by  letting  the 
vibrating  prongs  touch  the  surface  of  water.  3.  Pluck  a  string  of  a 
guitar  or  violin,  and  find  proof  that  it  is  vibrating  while  giving  out 
sound. 

To  show  the  Transmission  of  Sound.  —  i .  Vibrate  a  tuning  fork 
and  press  the  stem  against  a  table  or  desk.  The  vibrations  which  are 
reenforced  in  this  way  will  be  heard  in  all  parts  of  the  room.  Now 
press  one  end  of  a  wooden  rod,  as  a  broom  handle,  against  the  table, 
and  bring  the  stem  of  the  vibrating  fork  against  the  other  end.  The 
vibrations  now  move  down  the  stick  to  the  table,  from  whence  they 
are  communicated  to  the  air.  Observe  that  the  sound  waves,  to  reach 
the  ear,  must  pass  through  the  rod,  the  table,  and  the  air.  2.  Fasten 
the  timing  fork  to  a  flat  piece  of  cork  by  pressing  the  stem  into  a  small 
hole  in  the  center.  Vibrate  the  fork  and  let  the  cork  rest  on  the  sur- 
face of  water  in  a  half-filled  tumbler  on  the  table.  The  sound  will,  as 
before,  pass  to  the  table  and  then  to  the  air.  Observe  that  in  this  case 
the  vibrations  are  transmitted  by  a  liquid,  a  solid,  and  by  the  air. 


368  COORDINATION    AND    SENSATION 

Compare  this  action  with  the  transmission  of  sound  waves  by  different 
portions  of  the  ear. 

To  show  Effects  of  Sound  Waves.  —  I.  Place  two  large  tuning 
forks  of  the  same  pitch,  and  mounte:1:  on  thin  boxes  for  reenforcing 
their  vibrations,  near  each  other  on  a  table.  Vibrate  one  of  the  forks 
for  a  moment  and  then  stop  it  by  means  of  the  hand.  Observe  that 
the  other  fork  has  been  set  in  vibration.  (This  experiment  does  not 
work  with  forks  of  different  pitch.)  2.  While  holding  a  thin  piece  of 
paper  against  a  comb  with  the  open  lips,  produce  musical  tones  with 
the  vocal  cords.  These  will  set  the  paper  in  vibration,  producing  the 
so-called  "  comb  music."  3.  Examine  the  disk  in  a  telephone  which  is 
set  in  vibration  by  the  voice.  Observe  that  it  is  a  thin  disk  and,  like 
the  membrane  of  the  ear,  has  air  on  both  sides  of  it. 

To  show  the  Reinforcement  of  Sound.  —  I.  Vibrate  a  tuning  fork 
in  the  air,  noting  the  feebleness  of  the  tone  produced.  Then  hold  the 
stem  against  a  door  or  the  top  of  a  table,  noting  the  difference. 
2.  Hold  a  vibrating  tuning  fork  over  a  tall  jar,  or  bottle,  and  gradually 
add  water.  If  the  vessel  is  sufficiently  tall,  a  depth  will  be  reached 
where  the  air  in  the  vessel  reenforces  the  sound  from  the  fork.  3. 
Hold  a  vibrating  fork  over  the  mouth  of  a  small  fruit  jar,  partly  covered 
with  a  piece  of  cardboard.  By  varying  the  size  of  the  opening,  a  posi- 
tion will  be  found  where  the  sound  is  reenforced.  If  not  successful  at 
first,  try  bottles  and  jars  of  different  sizes. 

To  illustrate  the  Manner  of  Vibration  of  the  Liquid  in  the  Internal 
Ear.  —  Tie  a  piece  of  dental  rubber  over  the  end  of  a  glass  or  wooden 
tube  about  half  an  inch  in  diameter  and  six  inches  in  length.  Fill  the 
tube  entirely  full  of  water  and,  without  spilling,  tie  a  piece  of  thin  rub- 
ber tightly  over  the  other  end.  Holding  the  tube  horizontally,  press 
the  rubber  in  at  one  end  and  note  that  it  is  pushed  out  at  the  other 
end.  Make  an  imitation  of  a  vibration  with  the  finger  against  the 
rubber  at  one  end  of  the  tube  and  note  the  effect  at  the  other  end. 
To  what  do  the  tube  and  the  rubber  on  the 
ends  of  the  tube  correspond  in  the  internal 
ear? 

To  show  the  Plan  of  the  Larynx.  —  Cut 
from   stiff   paper    four  pieces   of   different 

FIG.  156. —  Simple  ap-  shapes  as  indicated  in  Fig.  156.  (The 
paratus  for  demonstrating  piece  to  the  left  should  have  a  length  of 
the  larynx.  about  six  inches,  the  others  proportionally 


THE  LARYNX  AND  THE  EAR         369 

large.)  The  largest  represents  the  thyroid  cartilage,  the  next  in  size 
the  cricoid,  and  the  two  smallest  the  arytenoid  cartilages.  By  means 
of  pins,  or  threads,  connect  these  with  each  other  according  to  the  de- 
scription of  the  larynx  on  page  253.  With  this  simple  model  the  move- 
ments of  the  different  cartilages  and  their  effect  upon  the  vocal  cords 
may  be  illustrated. 

To  show  the  Relation  of  the  Movements  of  the  Vocal  Organs  to  the 
Production  of  Different  Sounds.  —  i .  Lightly  grasp  the  larynx  with  the 
fingers  while  talking.  Observe  the  changes,  both  in  the  position  and 
shape  of  the  larynx,  in  the  production  of  sounds  of  different  pitch. 
2.  Observe  the  difference  in  the  action  of  the  muscles  of  respiration  in 
the  production  of  loud  and  faint  sounds.  3.  Pronounce  slowly  the 
vowels,  A,  E,  I,  O,  U,  and  the  consonants  C,  F,  K,  M,  R,  S,  T,  and 
V,  noting  the  shape  of  the  mouth,  the  position  of  the  tongue,  and  the 
action  of  the  lips  in  each  case. 

To  demonstrate  the  Ear.  —  Examine  a  dissectible  model  of  the  ear, 
locating  and  naming  the  different  parts.  Trace  as  far  as  possible  the 
path  of  the  sound  waves  and  find  the  termination  of  the  auditory  nerve. 
Note  also  the  relative  size  of  the  parts,  and  calculate  the  number  of  times 
the  model  is  larger  than  the  natural  ear.  Suggestion :  The  greatest 
diameter  of  the  internal  ear  is  about  three  fourths  of  an  inch. 

In  an  extended  course  it  is  a  profitable  exercise  to  dissect  the  ear  of 
a  sheep  or  calf,  observing  the  auditory  canal,  middle  ear,  bridge  of 
bones,  and  the  tympanic  membrane  with  attached  malleus  and  tensor 
tympanic  muscle.  Pass  a  probe  from  the  nasal  pharynx  through  the 
Eustachian  tube  into  the  middle  ear.  With  bone  forceps  or  a  fine  saw, 
split  open  the  petrous  portion  of  the  temporal  bone  and  observe  the 
cochlea  and  the  semicircular  canals.  By  a  careful  dissection  other 
parts  of  interest  may  also  be  shown. 


CHAPTER  XXII 
THE  EYE 

SIGHT  is  considered  the  most  important  of  the  sensations 
It  is  the  chief  means  of  bringing  the  body  into  proper  re- 
lations with  its  surroundings  and,  even  more  than  the  sen- 
sation of  hearing,  is  an  avenue  for  the  reception  of  ideas. 
The  sense  organs  for  the  production  of  sight  are  the  eyes ; 
the  external  stimulus  is 

Light.  —  Light,  like  sound,  consists  of  certain  vibrating 
movements,  or  waves.  They  differ  from  sound  waves, 
however,  in  form,  velocity,  and  in  method  of  origin  and 
transmission.  Light  waves  are  able  to  pass  through  a 
vacuum,  thus  showing  that  they  are  not  dependent  upon 
air  for  their  transmission.  They  are  supposed  to  be  trans- 
mitted by  what  the  physicist  calls  ether — a  highly  elastic 
and  exceedingly  thin  substance  which  fills  all  space  and 
penetrates  all  matter.  As  a  rule,  light  waves  originate  in 
bodies  that  are  highly  heated,  being  started  by  the  vibra- 
tions of  the  minute  particles  of  matter. 

Light  is  influenced  in  its  movements  by  various  conditions.  In  a 
substance  of  uniform  df  E*JJ|J  it  moves  with  an  unchanging  velocity  and 
in  a  straight  fine.  If  it  enters  a  less  dense,  or  rarer,  substance,  its  ve- 
locity increases :  if  one  more  dense,  its  Telocity  diminishes ;  and  if  it 
enters  either  the  rarer  or  denser  substance  in  any  direction  other  than 
perpendicularly,  it  is  bent  out  of  its  coarse,  or  refracted.  If  it  strikes 
jgjJH-U  a  body  tying;  in  its  coarse,  it  may  be  thrown  off  (reflected),  or 
it  may  enter  the  body  and  either  be  passed  on  through  (transmitted) 
or  absorbed  (Fig.  157).  Light  which  is  absorbed  is  transformed  into 
beat 


THE  EYE 


37' 


Kinds  of  Reflection.  — Waves  of  light  striking  against  the  smooth 
surface  of  a  mirror  are  thrown  oft  in  definite  directions,  depending  on 
the  angle  at  which  they  strike.  (Illustrate  by  holding  a  mirror  in  the 
direct  rays  of  the  sun.)  But  light  waves  that  strike  rough  surfaces  are 
reflected  in  practically  all  directions  and  apparently  without  reference  to 


FIG.  157.  —  Diagram  illustrating  passage  of  light  wares.  On  the  right 
the  light  is  transmitted  by  the  glass,  reflected  by  the  mirror,  refracted  bj  the 
prism,  and  absorbed  by  the  black  cloth.  On  the  left  the  light  from  the 
candle  forms  an  image  by  passing  through  a  small  hole  in  a  cardboard  and 
falling  upon  a  screen. 

the  angle  at  which  they  strike.  (Illustrate  by  placing  a  piece  of  white 
paper  in  the  direct  rays  of  the  sun.  It  matters  not  from  what  direction 
it  is  viewed,  waves  of  light  strike  the  eye.)  This  kind  of  reflection  is 
called  diffusion,  and  it  serves  the  important  purpose  of  making  objects 
visible.  The  light  waves  passing  out  in  all  directions  from  objects 
which  have  received  light  from  the  sun,  or  some  other  luminous  body, 
enable  them  to  be  seen. 

Formation  of  Images.  —  Another  principle  necessary  to 
seeing  is  that  of  refraction.  Refraction  means  the  bend- 
ing, or  turning,  of  light  from  a  straight  course.  One  of 
the  most  interesting  effects  of  refraction  is  the  formation 
of  images  of  objects,  such  as  may  be  accomplished  by  light 
from  them  passing  in  a  certain  manner  through  con  vex  lenses. 
If,  for  example,  a  convex  lens  be  moved  back  and  forth 


372 


COORDINATION    AND    SENSATION 


between  a  candle  and  a  screen  in  a  dimly  lighted  room,  a 
position  will  bi  found  where  a  picture  of  the  candle  falls 
upon  the  screen.  This  picture,  called  the  image,  results 
from  the  refraction  of  the  candle  light  in  passing  through 
the  lens. 


Image 


FIG.  158. — Diagram  illustrating  formation  of  images.  On  the  right 
the  image  is  formed  by  a  double  convex  lens;  on  the  left  by  the  lenses  of  the 
eye.  The  candle  flame  represents  a  luminous,  or  light-giving,  body;  but  light 
passes  from  the  large  arrow  by  reflection.  (See  text.) 

In  order  to  form  an  image,  the  light  waves  spreading  out  from  the 
object  must  be  brought  together,  or*focused.  Focusing  means  literally 
the  bringing  of  light  to  a  point,  but  it  is  evident  in  the  formation  of  an 
image  that  all  the  waves  are  not  brought  to  a  single  point.  If  they 
were,  there  would  be  no  image.  In  the  example  of  the  candle  given 
above,  the  explanation  is  as  follows  : 

The  light  from  the  candle  comes  from  a  great  number  of  separate 
and  distinct  points  in  the  candle  flame.  The  lens,  by  its  peculiar  shape, 
bends  the  waves  coming  from  any  single  point  so  that  they  are  brought 
to  a  corresponding  point  on  the  screen.  Furthermore,  the  points  of 
focused  light  are  made  to  occupy  the  same  relative  positions  on  the 
screen  as  the  points  from  which  they  emanate  in  the  candle  flame 
(Fig.  158).  This  is  why  the  area  of  light  on  the  screen  has  the  same 
form  as  the  candle,  or  makes  an  image  of  it.  The  same  explanation 
applies  if,  instead  of  the  luminous  candle,  a  body  that  simply  reflects 
light,  as  a  book,  is  used. 

The  Problem  of  Seeing.  —  What  we  call  seeing  is  vastly 
more  than  the  stimulation  of  the  brain  through  the  action 
of  light  upon  afferent  neurons.  It  is  the  perceiving  of  all 
the  different  things  that  make  up  our  surroundings.  If 


THE   EYE 


373 


one  looks  toward  the  clear  sky,  he  receives  a  sensation 
of  light,  but  sees  no  object.  He  may  also  get  a  sensa- 
tion of  light  with  the  eyelids  closed,  if  he  turn  the  eyes 
toward  the  window  or  some  bright  light.  But  how  differ- 
ent when  the  light  from  various  objects  enters  the  eyes. 
There  is  apparently  no  consciousness  of  light,  but  instead 
a  consciousness  of  the  size,  form,  color,  and  position  of  the 
objects.  Seeing  is  perceiving  objects.  Stimulation  by  the 
light  waves  is  only  the  means  toward  this  end.  The  chief 
problem  in  the  study  of  sight  is  that  of  determining  how 
light  waves  enable  us  to  become  conscious  of  objects. 

Sense  Organs  of  Sight.  —  The  sense  organs  of  sight  con- 
sist mainly  of  the  two  eyeballs.  Each  of  these  is  located 
in  a  cavity  of  the  skull  bones,  called  the  orbit,  where  it  is 
held  in  position  by  suitable  tissues  and  turned  in  different 
directions  by  a  special  set  of  muscles.-  A  cup-shaped 
receptacle  is  provided  within  the  orbit,  by  layers  of  fat, 
and  a  smooth  surface  is  supplied  by  a  double  membrane 
that  lies  between  the  fat  and  the  eyeball.  In  front  the 
eyeballs  are  provided  with  movable  coverings,  called  the 
eyelids.  These  are  composed  of  dense  layers  of  connec- 
tive tissue,  covered  on  the  outside  by  the  skin  and  lined 
within  by  a  sensitive  membrane,  called  the  conjunctiva. 
At  the  base  of  the  lids  the  conjunctiva  passes  to  the  eye- 
ball and  forms  a  firmly  attached  covering  over  its  front 
surface.  This  membrane  prevents  the  passage  of  foreign 
materials  back  of  the  eyeball,  and  by  its  sensitiveness 
stimulates  effort  for  the  removal  of  irritating  substances 
from  beneath  the  lids.  The  eyelashes  and  the  eyebrows 
are  also  a  means  of  protecting  the  eyeballs. 

The  Eyeball,  or  globe  of  the  eye,  is  a  device  tor  focusing 
light  upon  a  sensitized  nervous  surface  which  it  incloses 
and  protects.  In  shape  it  is  nearly  spherical,  being,  about 


374 


an  inch  in  diameter  from  right  to  left  and  nine  tenths  of 
an  inch  both  in  its  vertical  diameter  and  from  front  to 
back.  It  has  the  appearance  of  having  been  formed  by 

the  union  of  two  spheri- 
cal segments  of  differ- 
ent size.  The  smaller 
segment,  which  forms 
about  one  sixth  of  the 
whole,  is  set  upon  the 
larger  and  forms  the 
projecting  transparent 
portion  in  front.  The 
walls  of  the  eyeballs 
are  made  up  of  three 
separate  layers,  or 
coats  —  an  outer  coat, 
a  middle  coat,  and  an 
inner  coat  (Fig.  1 59). 

FIG.   159. —Diagram  of  the  eyeball  in        The  Outer  C°at  sur- 
position.    i.  Yellow  spot.    2.  Blind  spot,  rounds  the  entire  globe 

3.    Retina.      4.    Choroid   coat.      5.   Sclerotic  of  the  eye  and  consists 

coat.    6.  Crystalline  lens.    7.  Suspensory  liga-  Q£       twQ  tg the 

ment.    8.  Ciliary  processes  and  ciliary  muscle. 

9.    Iris   containing    the   pupil.       10.   Cornea,  sclerotic    Coat   and    the 

ii.  Lymph  duct.    12.  Conjunctiva.    13.  In-  cornea.     The  sclerotic 

ferior  and  superior  recti  muscles.     14.  Optic  coaf  covers  the  greater 

nerve.  15.  Elevator  muscle  of  eyelid  16.  Bone.  i(m  Q£  ^  j  r 
A.  Posterior  chamber  containing  the  vitreous 

humor.     B.  Anterior  chamber  containing  the  spherical  segment  and 

aqueous  humor.  is  recognized  in  front 

as   "  the  white  of  the 

eye."  It  is  composed  mainly  of  fibrous  connective  tissue 
and  is  dense,  opaque,  and  tough.  It  preserves  the  form 
of  the  eyeball  and  protects  the  portions  within.  It  is 
pierced  at  the  back  by  a  small  opening  which  admits  the 


THE   EYE  375 

optic  nerve,  and  in  front  it  becomes  changed  into  the 
peculiar  tissue  that  makes  up  the  cornea. 

The  cornea  forms  the  transparent  covering  over  the 
lesser  spherical  segment  of  the  eyeball,  shading  into  the 
sclerotic  coat  at  its  edges.  It  has  a  complex  structure, 
consisting  in  the  main  of  a  transparent  form  of  connective 
tissue.  It  serves  the  purpose  of  admitting  light  into  the 
eyeball. 

The  Middle  Coat  consists  of  three  connected  portions  — 
the  choroid  coat,  the  ciliary  processes,  and  the  iris.  These 
surround  the  larger  spherical  segment.  All  three  parts 
are  rich  in  blood  vessels,  containing  the  blood  supply  to 
the  greater  portion  of  the  eyeball. 

The  choroid  coat  lies  immediately  beneath  the  sclerotic 
coat  at  all  places  except  a  small  margin  toward  the  front 
of  the  eyeball.  It  is  composed  chiefly  of  blood  vessels 
and  a  delicate  form  of  connective  tissue  that  holds  them  in 
place.  It  contains  numerous  pigment  cells  which  give  it 
a  dark  appearance  and  serve  to  absorb  surplus  light.  Near 
where  the  sclerotic  coat  joins  the  cornea,  the  choroid  coat 
separates  from  the  outer  wall  and,  by  folding,  forms  many 
slight  projections  into  the  interior  space.  These  are  known 
as  the  ciliary  processes.  The  effect  of  these  folds  is  to  col- 
lect a  large  number  of  capillaries  into  a  small  space  and 
to  give  this  part  of  the  eyeball  an  extra  supply  of  blood. 
Between  the  ciliary  processes  and  the  sclerotic  coat  is  a 
small  muscle,  containing  both  circular  and  longitudinal 
fibers,  called  the  ciliary  muscle. 

The  iris  is  a  continuation  of  the  choroid  coat  across  the 
front  of  the  eyeball.  It  forms  a  dividing  curtain  between 
the  two  spherical  segments  and  gives  the  color  to  the  eye. 
At  its  center  is  a  circular  opening,  called  the  ptipil,  which 
admits  light  to  the  back  of  the  eyeball.  By  varying  the 


376 


COORDINATION    AND    SENSATION 


size  of  the  pupil,  the  iris  is  able  to  regulate  the  amount  of 
light  which  passes  through  and  it  employs  for  this  pur- 
pose two  sets  of  muscular  fibers.  One  set  of  fibers 
forms  a  thin  band  which  encircles  the  pupil  and  serves 
as  a  sphincter  to  diminish  the  opening.  Opposing  this  are 
radiating  fibers  which  are  attached  between  the  inner  and 
outer  margins  of  the  iris.  By  their  contraction  the  size  of 
the  opening  is  increased.  Both  sets  of  fibers  act  reflex- 
ively  and  are  stimulated  by  variations  in  the  light  falling 
upon  the  retina. 


FIG.  160.  —  Diagram  showing  main  nervous  elements  in  the  retina. 

Light  waves  stimulate  the  rods  and  cones  at  back  surface  of  the  retina,  start- 
ing impulses  which  excite  the  ganglion  cells  at  the  front  surface.  Fibers  from 
the  ganglion  cells  pass  into  the  optic  nerve. 

The  Inner  Coat,  or  Retina.  —  This  is  a  delicate  membrane 
containing  the  expanded  termination  of  the  optic  nerve. 
It  rests  upon  the  choroid  coat  and  spreads  over  about 
two  thirds  of  the  back  surface  of  the  eyeball.  Although 
not  more  than  one  fiftieth  of  an  inch  in  thickness,  it  pre- 
sents a  very  complex  structure,  essentially  nervous,  and  is 


THE   EYE 


377 


made  up  of  several  distinct  layers.  Of  chief  importance 
in  the  outer  layer  are  the  cells  which  are  acted  upon 
directly  by  the  light  and  are  named,  from  their  shape, 
the  rods  and  cones.  In  contact  with  these,  but  occupying 
a  separate  layer,  are  the  ends  of  small  afferent  nerve  cells. 
These  in  turn  communicate  with  nerve  cells  in  a  third 
layer,  known  as  the  ganglion  cells,  that  send  their  fibers 
into  the  optic  nerve  (Fig.  160). 

In  the  center  of  the  retina  is  a  slight  oval  depression 
having  a  faint  yellowish  color,  and  called,  on  that  account, 
the  yellow  spot.  This  is  the  part  of  the  retina  which  is 
most  sensitive  to  light.  Directly  over  the  place  of  en- 
trance of  the  optic  nerve  is  a  small  area  from  which  the 
rods  and  cones  are  absent  and  which,  therefore,  is  not 
sensitive  to  light.  This  is  called  the  blind  spot.  (See 
Practical  Work.) 

The  Crystalline  Lens.  —  Immediately  back  of  the  iris 
and  touching  it  is  a  transparent,  rounded  body,  called  the 
crystalline  lens.  This  is  about  one  fourth  of  an  inch 
thick  and  one  third  of  an  inch  through  its  long  diameter, 
and  is  more  curved  on  the  back  than  on  the  front  surface. 
It  is  inclosed  in  a  thin  sheath,  called  the  membranous  cap- 
sule, which  connects  with  a  divided  sheath  from  the  sides 
of  the  eyeball,  called  the  suspensory  ligament  (Fig.  159). 
Both  the  lens  and  the  capsule  are  highly  elastic. 

Chambers  and  "Humors"  of  the  Eyeball.  — The  crystal- 
line lens  together  with  the  suspensory  ligament  and  the 
ciliary  processes  form. a  partition  across  the  eyeball.  This 
divides  the  eye  space  into  two  separate  compartments, 
which  are  filled  with  the  so-called  "  humors "  of  the  eye. 
The  front  cavity  of  the  eyeball,  which  is  again  divided  in 
part  by  the  iris,  is  filled  with  the  aqueous  humor.  This 
is  a  clear,  lymph-like  liquid  which  contains  an  occa- 


378  COORDINATION   AND   SENSATION 

sional  white  corpuscle.  It  has  a  feeble  motion  and  is 
slowly  added  to  and  withdrawn  from  the  eye.  It  is  sup- 
plied mainly  by  the  blood  vessels  in  the  ciliary  processes 
and  finds  a  place  of  exit  through  a  small  lymph  duct  at 
the  edge  of  the  cornea  (Fig.  159). 

The  back  portion  of  the  eyeball  is  filled  with  a  soft, 
transparent,  jelly-like  substance,  called  the  vitreous  humor. 
It  is  in  contact  with  the  surface  of  the  retina  at  the  back 
and  with  the  attachments  of  the  lens  in  front,  being  sur- 
rounded by  a  thin  covering  of  its  own,  called  the  hyaloid 
membrane.  The  aqueous  and  vitreous  humors  aid  in  keep- 
ing the  eyeball  in  shape  and  also  in  focusing. 

How  we  see  Objects.  —  To  see  an  object  at  least  four 
things  must  happen : 

1.  Light  must  pass  from  the  object  into  the  eye.    Objects 
cannot  be  seen  where  there  is  no  light  or  where,  for  some 
reason,  it  is  kept  from  entering  the  eye. 

2.  The  light  from  the  object  must  be  focused  (made  to 
form  an  image)  on  the  retina.     In  forming  the  image,  an 
area  of  the  retina  is  stimulated  which  corresponds  to  the 
form  of  the  object. 

3.  Impulses   must  pass  from  the  retina  to  the  brain, 
stimulating  if  to  produce  the  sensations. 

4.  The  sensations  must  be  so  interpreted  by  the  mind 
as  to  give  an  impression  of  the  object. 

Focusing  Power  of  the  Eyeball.  —  The  eyeball  is  essen- 
tially a  device  for  focusing  light.  All  of  its  transparent 
portions  are  directly  concerned  in  this  work,  and  the 
portions  that  are  not  transparent  serve  to  protect  and 
operate  these  parts  and  hold  them  in  place.  Of  chief 
importance  are  the  crystalline  lens  and  the  cornea. 
Both  of  these  are  lenses.  The  cornea  with  its  inclosed 
liquid  is  a  plano-convex  lens,  while  the  crystalline  lens  is 


THE  EYE 


double  convex.1  Because  of  the  great  difference  in  density 
between  the  air  on  the  outside  and  the  aqueous  humor 
within,  the  cornea  is  the  more  powerful  of  the  two.  The 
crystalline  lens,  however,  performs  a  special  work  in 
focusing  which  is  of  great  importance.  The  iris  also  aids 
in  focusing  since  it,  through  the  pupil,  regulates  the  amount 
of  light  entering  the  back  chamber  of  the  eyeball  and 
causes  it  to  fall  in  the  center  of  the  crystalline  lens,  the 
part  which  focuses  most  accurately. 

Accommodation.  —  A  difficulty  in  focusing  arises  from 
the  fact  that  the  degree  of  divergence  of  the  light  waves 


DISTANT 


FIG.  161.  — Diagram  showing  changes  in  shape  of  crystalline  lens 
to  adapt  it  to  near  and  distant  vision. 

entering  the  eye  from  different  objects,  varies  according 
to  their  distance.  Since  the  waves  from  any  given  point 
on  an  object  pass  out  in  straight  lines  in  all  directions, 
the  waves  that  enter  the  eye  from  distant  objects  are  at 
a  different  angle  from  those  that  enter  from  near  objects. 
In  reality  waves  from  distant  objects  are  practically  parallel, 
while  those  from  very  near  objects  diverge  to  a  consider- 
able degree.  To  adjust  the  eye  to  different  distances 
requires  some  change  in  the  focusing  parts  that  corre- 
sponds to  the  differences  in  the  divergence  of  the  light. 

1  Consult  some  work  on  physics  on  the  different  kinds  of  lenses  and  their 
uses. 


380  COORDINATION    AND    SENSATION 

This  change,  called  accommodation,  occurs  in  the  crystal- 
line lens.1  In  the  process  of  accommodation,  changes 
occur  in  the  shape  of  the  crystalline  lens,  as  follows : 

1.  In  looking  from  a  distant  to  a  near  object,  the  lens 
becomes  more  convex,  i.e.,  rounder  and  thicker  (Fig.  161). 
This  change  is  necessary  because  the  greater  divergence 
of  the  light  from  the  near  objects  requires  a  greater  con- 
verging power  on  the  part  of  the  lens.2 

2.  In  looking   from    near   to  distant  objects,  the  lens 
becomes  flatter  and  thinner  (Fig.  161).     This   change  is 
necessary  because  the  less  divergent  waves  from  the  dis- 
tant objects  require  less  converging  power  on  the  part  of 
the  lens. 

The  method  employed  in  changing  the  shape  of  the  lens  is  difficult 
to  determine  and  different  theories  have  been  advanced  to  account  for 
it.  The  following,  proposed  by  Helmholtz,  is  the  theory  most  generally 
accepted : 

The  lens  is  held  in  place  back  of  the  pupil  by  the  suspensory  liga- 
ment. This  is  attached  at  its  inner  margin  to  the  membranous  capsule, 
and  at  its  outer  margin  to  the  sides  of  the  eyeball,  and  entirely  sur- 
rounds the  lens.  It  is  drawn  perfectly  tight  so  that  the  sides  of  the 
eyeball  exert  a  continuous  tension,  or  pull,  on  the  membranous  capsule, 
which,  in  its  turn,  exerts  pressure  on  the  sides  of  the  lens,  tending  to 
flatten  it.  This  arrangement  brings  the  elastic  force  of  the  eyeball  into 
opposition  to  the  elastic  force  of  the  lens.  The  ciliary  muscle  plays 
between  these  opposing  forces  in  the  following  manner: 

To  thicken  the  lens,  the  ciliary  muscle  contracts,  pulling  forward 
the  suspensory  ligament  and  releasing  its  tension  on  the  membranous 

1  Wiih  respect  to  its  adjustments  the  eye  does  not  differ  in  principle  from  vari- 
ous other  optical  instruments,  such  as  the  microscope,  telescope,  photographer's 
camera,  etc.,  which,  in  their  use,  form  images  of  objects.     These  all  require  some 
adjustment  of  their  parts,  called  focusing,  which  adapts  them   to  the  distance. 
The  eye's  method  of  focusing,  however,  differs  from  that  of  most  optical  instru- 
ments, in  that  the  adjustment  is  brought  about  through  changes  in  the  curvature 
of  a  lens. 

2  The  converging  power  of  convex  lenses  varies  as  the  curvature  —  the  greater 
the  curvature,  the  greater  the  converging  power. 


THE   EYE 


381 


capsule.  This  enables  the  lens  to  thicken  on  account  of  its  own  elastic 
force.  To  flatten  the  lens,  the  ciliary  muscle  relaxes,  the  elastic  force 
of  the  eyeball  resumes  its  tension  on  the  suspensory  ligament,  and  the 
membranous  capsule  resumes  its  pressure  on  the  sides  of  the  lens. 
This  pressure,  overcoming  the  elastic  force  of  the  lens,  flattens  it. 

Movements  of  the  Eyeballs.  —  In  order  that  the  light 
may  enter  the  eyeballs  to  the  best  advantage,  they  must 
be  moved  in  various  directions.  These  movements  are 
brought  about  through  the  action  of  six  small  muscles 
attached  to  each  eyeball.  Four  of  these,  named,  from 


Superior 


ffx  ternaf. 
rec-fus 


Superior  / 
recCus 


ternal 
rectua 


Optic  nerve 


FIG.  162.  —  Exterior  muscles  of  eyeball. 


their  positions,  the  superior,  inferior,  internal,  and  external 
recti  muscles,  are  attached  at  one  end  to  the  sides  of  the 
eyeball  and  at  the  other  end  to  the  back  of  the  orbit 
(Fig.  162).  These,  in  the  order  named,  turn  the  eyes  up- 
ward, downward,  inward,  and  outward.  The  other  two, 
the  superior  and  inferior  oblique  muscles,  aid  in  certain 
movements  of  the  recti  muscles  and,  in  addition,  serve  to 
rotate  the  eyes  slightly.  The  movements  of  the  eyeballs 
are  similar  to  those  of  ball  and  socket  joints. 

Binocular  Vision.  —  In  addition   to   directing  the  eyeballs  so  that 
light  may  enter  them  to  the  best  advantage  from  different  objects,  the 


382  COORDINATION   AND    SENSATION 

muscles  also  enable  two  eyes  to  be  used  as  one.  Whenever  the  eyes 
are  directed  toward  the  same  object,  an  image  of  this  object  is  formed 
on  the  retina  of  each.  Double  vision  is  prevented  only  by  having  the 
images  fall  on  corresponding  places  in  the  two  eyes.  This  is  accom- 
plished by  the  muscles.  In  each  act  of  seeing,  it  becomes  the  task 
of  the  superior  and  inferior  recti  muscles  to  keep  the  eyes  in  the 
same  plane,  and  of  the  external  and  internal  recti  muscles  to  give 
just  the  right  amount  of  convergence.  If  slight  pressure  is  exerted 
against  one  of  the  eyes,  the  action  of  the  muscles  is  interfered  with 
and,  as  a  consequence,  one  sees  double.  The  advantages  of  two 
eyes  over  one  in  seeing  lie  in  the  greater  distinctness  and  broader 
range  of  vision  and  in  the  greater  correctness  of  judgments  of 
distance. 

Visual  Sensations.  —  The  visual  sensations  include  those  of  color 
and  those  of  a  general  sensibility  to  light.  Proof  of  the  existence  of 
these  types  of  sensation  is  found  in  color  blindness,  a  defect  which 
renders  the  individual  unable  to  distinguish  certain  colors  when  he  is 
still  able  to  see  objects.  Color  sensations  are  the  results  of  light  waves 
of  different  lengths  acting  on  the  retina.  While  the  method  by  which 
waves  of  one  length  produce  one  kind  of  sensation  and  those  of  another 
length  a  different  sensation  is  not  understood,  the  cones  appear  to  be  the 
portions  of  the  retina  acted  on  to  produce  the  color.  On  the  other 
hand,  the  rods  are  sensitive  to  all  wave  lengths  and  give  general  sensi- 
bility to  light. 

Visual  Perceptions.  —  "  Seeing  "  is  very  largely  the  mental  interpreta- 
tion of  the  primary  sensations  and  the  conditions  under  which  they 
occur.  For  example,  our  ability  to  see  objects  in  their  natural  positions 
when  their  images  are  inverted  on  the  retina  is  explained  by  the  fact 
that  we  are  not  conscious  of  the  retinal  image,  but  of  the  mind's  inter- 
pretation of  it  through  experience.  Experience  has  also  taught  us  to 
locate  objects  in  the  direction  toward  which  it  is  necessary  to  turn  the 
eyes  in  order  to  see  them.  In  other  words,  we  see  objects  in  the  direc- 
tion from  which  the  light  enters  the  eyes.  That  the  object  is  not  always 
in  that  direction  is  shown  by  the  image  in  the  mirror.  The  apparent 
size  and  form  of  objects  are  inferences,  and  they  are  based  in  part 
upon  the  size  and  form  of  the  area  of  the  retina  stimulated.  We  judge 
of  distance  by  the  effort  required  to  converge  the  eyes  upon  the  objects, 
by  the  amount  of  divergence  of  the  waves  entering  the  pupil,  and  also 
by  the  apparent  size  of  the  object. 


THE  EYE 


383 


•z^— ^Lachrymal 


The  Lachrymal  Apparatus.  —  Seeing  requires  that  the 
light  penetrate  to  the  retina.  For  this  reason  all  the 
structures  in  front  of  the  retina  are  transparent.  One  of 
these  structures,  the  cornea,  on  account  of  its  exposure  to 
the  air,  is  liable  to  become  dry,  like  the  skin,  and  to  lose  its 
transparency.  To  preserve  the  transparency  of  the  cornea, 
and  also  to  lubricate  the  eyelids  and 
aid  in  the  removal  of  foreign  bodies, 
a  secretion,  called  tears,  is  constantly 
supplied. 

The  lachrymal,  or  tear,  glands  are 
situated  at  the  upper  and  outer 
margins  of  the  orbits.  They  have 
the  general  structure  of  the  salivary 
glands  and  discharge  their  liquid  by 

small  ducts  beneath  the  upper  lids.       Fia  r63-~  Diagram  of 
T^  ,  ,,  irrigating    system  of   the 

From  here  the  tears  spread  over  the  eye.    Affer  wyetting  the  eye. 

Surfaces    of    the    eyeballs    and    find    ball  the  tears  may  also  mois- 

their  way  in  each  eye  to  two  small  ten  the  air  entering  the 
canals  whose  openings  may  be  seen  lungs' 
on  the  edges  of  the  lids  near  the  inner  corner  (Fig.  163). 
These  canals  unite  to  form  the  nasal  duct,  which  conveys 
the  tears  to  the  nasal  cavity  on  the  same  side  of  the  nose. 
When  by  evaporation  the  eyeball  becomes  too  dry,  the 
lids  close  reflexively  and  spread  a  fresh  layer  of  tears  over 
the  surface.  Any  excess  is  passed  into  the  nostrils,  where 
it  aids  in  moistening  the  air  entering  the  lungs. 

HYGIENE  OF  THE   EYE 

Defects  in  Focusing. — The  delicacy  and  complexity  of 
the  sense  organs  of  sight  render  them  liable  to  a  number 
of  imperfections,  or  defects,  the  most  frequent  and  impor- 
tant being  those  of  focusing.  Such  defects  not  only  result 


384 


COORDINATION   AND   SENSATION 


in  the  imperfect  vision  of  objects,  but  they  throw  an  extra 
strain  upon  the  nervous  system  and  may  render  the  pro- 
cess of  seeing  exceedingly  painful. 

A  normal  eye  is  able,  when  relaxed,  to  focus  light  accu- 
rately from  objects  which  are  twenty  feet  or  more  away 
and  to  accommodate  itself  to  objects  as  near  as  five  inches. 

An  eye  is  said  to  be  myopic,  or 
short-sighted,  when  it  is  unable 
to  focus  light  waves  from  dis- 
tant objects,  but  can  only  dis- 
tinguish the  objects  which  are 
near  at  hand.  In  such  an  eye 
the  ball  is  too  long  for  the  con- 
verging power  of  the  lenses, 
and  the  image  is  formed  in  front 
of  the  retina  (C,  Fig.  164). 
A  long-sighted,  or  hyper- 

metropic,  eye  is  one  which  can 
FIG.  164.  —  Diagrams  illustrat-     ..  ,.    .      f  ,.  .. 

ing  long-sightedness  and  short-  f°CUS  hSht  fr°m  dlstant  obJGCtS' 
sightedness,  and  method  of  but  not  from  near  objects.  In 

remedying  these  defects  by  lenses,  such  an  eye  the  ball  IS  too  short 
A.  Normal  eye.  B.  Long-sighted  f  Qr  the  converging  power  of  the 
eye.  C.  Short-sighted  eye.  i  i  • 

lenses  and  the  image  tends  to 

form  back  of  the  retina  (B,  Fig.  164).  These  defects  in 
focusing  are  remedied  by  wearing  glasses  with  lenses  so 
shaped  as  to  counteract  them.  Short-sightedness  is  cor- 
rected by  concave  lenses  and  long-sightedness  by  convex 
lenses,  as  shown  in  diagrams  above. 

Astigmatism  is  another  defect  in  the  focusing  power  of 
the  eye.  In  astigmatism  the  parts  of  the  eye  fail  to  form 
the  image  in  the  same  plane,  so  that  all  portions  of  the 
object  do  not  appear  equally  distinct.  Certain  parts  of  it 
are  indistinct,  or  blurred.  The  cause  is  found  in  some 


THE   EYE 


385 


difference  in  curvature  of  the  surfaces  of  the  cornea 
or  crystalline  lens.  It  is  corrected  by  lenses  so  ground 
as  to  correct  the  particular  defects  present  in  a  given 
eye. 

Whenever  defects  in  focusing  are  present,  particularly 
in  astigmatism,  extra  work  is  thrown  on  the  ciliary  muscle 
as  well  as  the  muscles  that  move  the  eyeballs.  The  result 
is  frequently  to  induce  a  condition,  known  as  muscle  iveak- 
ness,  which  renders  it  difficult  to  use  the  eyes.  Even  after 
the  defect  in  focusing  has  been  remedied,  the  muscles  re- 
cover slowly  and  must  be  used  with  care.  For  this  reason 
glasses  should  be  fitted  by  a  competent  oculist1  as  soon 
as  a  defect  is  known  to  exist.  When  one  is  unduly  nerv- 
ous, or  suffers  from  headache,  the  eyes  should  be  examined 
for  defects  in  focusing  (page  326). 

Eye  Strain  and  Disease.  —  The  extra  work  thrown  upon 
the  nervous  system  through  seeing  with  defective  eyes, 
especially  in  reading  and  other  close  work,  is  now  recog- 
nized as  an  important  cause  of  disease.  Through  the  tax 
made  upon  the  nervous  system  by  the  eyes,  there  may  be 
left  an  insufficient  amount  of  nervous  energy  for  the 
proper  running  of  the  vital  processes.  As  a  result  there 
is  a  decline  of  the  health.  Ample  proof  that  eye  strain 
interferes  with  the  vital  processes  and  causes  ill  health,  is 
found  in  the  improvements  that  result  when,  by  means  of 
glasses,  this  is  relieved. 

The  Eyes  of  School  Children.  —  School  children  often 
suffer  from  defects  of  vision  which  render  close  work  bur- 
densome, and  cause  headache,  general  nervousness,  and 
disease.  Furthermore,  the  visual  defects  may  be  unknown 
both  to  themselves  and  to  their  parents.  Pupils  showing 
indications  of  eye-strain  should  be  examined  by  an  oculist, 

1  An  oculist  is  a  physician  who  specializes  in  diseases  of  the  eye. 


386  COORDINATION    AND    SENSATION 

and  fitted  with  glasses  should  defects  be  discovered.1  The 
precaution,  adopted  by  many  schools,  of  having  the  eyes  of 
all  children  examined  by  a  competent  physician  employed 
for  the  purpose,  is  most  excellent  and  worthy  of  imitation. 

Reading  Glasses.  —  Many  people  whose  eyes  are  weak, 
because  slightly  defective,  find  great  relief  in  the  use  of 
special  glasses  for  reading  and  other  close  work.  By  using 
such  glasses  they  may  postpone  the  time  when  they  are 
compelled  to  wear  glasses  constantly.  It  is  in  the  close 
work  that  the  extra  strain  comes  upon  the  eyes,  and  if  this 
is  relieved,  one  can  much  better  withstand  the  work  of  dis- 
tant vision.  The  reading  glasses  should  be  fitted  by  a 
competent  oculist,  and  used  only  for  the  purpose  for  which 
they  are  intended. 

General  Precautions  in  the  Use  of  the  Eyes.  —  If 
proper  care  is  exercised  in  the  use  of  the  eyes,  many  of 
their  common  ailments  and  defects  may  be  avoided.  Any 
one,  whether  his  eyes  are  weak  or  strong,  will  do  well  to 
observe  the  following  precautions  : 

i.    Never  read  in  light  that  is  very  intense  or  very  dim. 

2.  When  the  eyes  hurt  from  reading,   stop   using  them. 

3.  Never  hold  a  book  so  that  the  smooth  page  reflects 
light  into  the  eyes.     The  best  way  is  to  sit  or  stand  so 
that   the    light    passes   over   the   shoulder   to   the   book. 

4.  Never  study  by  a  lamp  that  is  not  shaded.     5.    Prac- 
tice cleanliness  in  the  care  of  the  eyes.     Avoid  rubbing 
the   eyes  with   the    fingers   unless    sure   the    fingers   are 
clean. 

If  the  eyes  are  weak,  use  them  less  and  avoid,  if  pos- 
sible, reading  by  artificial  light.  Weak  eyes  are  some- 

1  Some  of  the  more  common  symptoms  of  eye  strain  are  nervousness,  headache, 
insomnia,  irritations  of  the  eyelids,  sensitiveness  to  bright  light,  and  pain  in  the 
use  of  the  eyes. 


THE   EYE 


387 


times  benefited  by  bathing  them  in  warm  water,  or  with 
water  containing  enough  salt  to  make  them  smart  slightly. 
Boracic  acid  dissolved  in  water  (40  grains  to  4  ounces  of 
distilled  water)  is  also  highly  recommended  as  a  wash  for 
weak.  eyes. 

Removal  of  Foreign  Bodies  from  the  Eyes.  —  Foreign 
bodies  embedded  in  the  eyeball  should  be  removed  by  the 
oculist  or  physician.  Small  particles  of  dust  or  cinder 
may  be  removed  without  the  aid 
of  the  physician,  by  exercising 
proper  care.  First  let  the  tears, 
if  possible,  wash  the  offending 
substance  to  the  corner  of  the 
eye,  or  edge  of  the  lid,  where  it 
can  be  removed  with  a  soft  cloth. 
If  it  sticks  to  the  ball  or  the  under 
surface  of  the  lid,  it  will  be  neces- 
sary to  find  where  it  is  located, 
and  then  dislodge  it  from  its  posi- 
'  tion.  Begin  by  examining  the 
lower  lid.  Pull  it  down  sufficiently 
to  expose  the  inner  surface,  and, 
if  the  foreign  substance  be  there,  wipe  it  off  with  the  hem 
of  a  clean  handkerchief.  If  it  is  not  under  the  lower  lid, 
it  will  be  necessary  to  fold  back  the  upper  lid.  "  The 
patient  is  told  to  look  down,  the  edge  of  the  lid  and  the 
lashes  are  seized  with  the  forefinger  and  thumb  of  the  right 
hand  (Fig.  165),  and  the  lid  is  drawn  at  first  downward  and 
forward  away  from  the  globe ;  then  upward  and  backward 
over  the  point  of  the  thumb  or  forefinger  of  the  left 
hand,  which  is  held  stationary  on  the  lid,  and  acts  as 
a  fulcrum." 1  The  foreign  body  is  now  removed  in 

1  Pyle,  Personal  Hygiene, 


FIG.  165.  —  Method  of  pro- 
cedure in  lifting  the  eyelid 
(Pyle). 


388  COORDINATION    AND    SENSATION 

the  same  manner  as  from  the  lower  lid.  A  large  lens 
may  be  used  to  good  advantage  in  finding  the  irritating 
substance. 

Strong  Chemicals  in  the  Eyes.  —  Students  in  the  lab- 
oratory frequently,  through  accident,  get  strong  chemicals, 
as  acids  and  bases,  in  the  eyes.  The  first  thing  to  do  in 
such  cases  is  quickly  and  thoroughly  to  flood  the  eyes  with 
water.  Any  of  the  chemical  which  remains  may  then  be 
counteracted  by  the  proper  reagent,  care  being  taken  to 
use  a  very  dilute  solution.  To  counteract  an  acid,  use 
sodium  bicarbonate  (cooking  soda),  and  for  bases  use  a 
very  dilute  solution  of  acetic  acid  (vinegar).  To  guard 
against  getting  the  counteractive  agent  too  strong  for  the 
inflamed  eye,  it  should  first  be  tried  on  an  eye  that  has  not 
been  injured. 

Summary.  —  The  nervous  impulses  that  cause  the  sen- 
sation of  sight  are  started  by  light  waves  falling  upon  a 
sensitized  nervous  surface,  called  the  retina.  By  means  of 
refractive  agents,  forming  a  part  of  the  eyeball  in  front  of 
the  retina,  light  from  different  objects  is  focused  and  made 
to  form  images  of  the  objects  upon  this  surface.  In  this 
way  the  light  is  made  to  stimulate  a  portion  of  the  retina 
corresponding  to  the  form  of  the  object.  This,  the  image 
method  of  stimulation,  enables  the  mind  to  recognize  objects 
and  to  locate  them  in  their  various  positions.  While  the 
greater  portion  of  the  eyeball  is  concerned  in  the  focusing  of 
light,  the  crystalline  lens,  operated  by  the  ciliary  muscle, 
serves  as  the  special  instrument  of  accommodation.  Muscles 
attached  to  the  eyeballs  turn  them  in  different  directions, 
and  so  adjust  them  with  reference  to  each  other  that 
double  vision  is  avoided. 

Exercises.  —  i.  Under  what  conditions  are  light  waves  reflected, 
refracted,  and  absorbed? 


THE  EYE  389 

2.  Why  does  the  body  not  need  a  light-producing  apparatus,  corre- 
sponding to  the  larynx  in  the  production  of  sound? 

3.  How  is  the  light  from  a  candle  made  to  form  an  image? 

4.  What  different  things  must  happen  in  order  that  one  may  see  an 
object  ? 

5.  Make  a  sectional  drawing  of  the  eyeball,  locating  and  naming  all 
the  parts. 

6.  Of  what  parts  are  the  outer,  middle,  and  inner  coats  of  the  eye- 
ball made  up? 

7.  What  portions  of  the  eyeball  reflect  light?     What  absorb  light? 
What  transmit  light?     What  refract  light? 

8.  Show  how  the  iris,  the  crystalline  lens,  the  retina,  the  ciliary 
muscle,  and  the  cornea  aid  in  seeing. 

9.  Trace  a  wave  of  light  from  a  visible  object  to  the  retina. 

10.  Why  does  not  the  inverted  image  on  the  retina  cause  us  to  see 
objects  upside  down  ? 

1 1 .  What  change  occurs  in  the  shape  of  the  crystalline  lens  when 
we  look  from  distant  to  near  objects  ?     From  near  to  distant  objects  ? 
Why  are  these  changes  necessary?     How  are  they  brought  about? 

12.  How  does  the  method  of  adjustment,  or  accommodation,  of  the 
eyeball  differ  from  that  of  a  telescope  or  a  photographer's  camera? 

13.  With  two  eyes  how  are  we  kept  from  seeing  double? 

14.  What  different  purposes  are  served  by  the  tears.     Trace  them 
from  the  lachrymalglands  to  the  nostrils. 

1 5 .  Show  how  the  proper  lenses  remedy  short-  and  long-sightedness. 

16.  Describe  the  conjunctiva  and  give  its  functions.     Why  should 
it  be  so  sensitive  ? 

17.  How  may  eye  strain  cause  disease  in  parts  of  the  body  remote 
from  the  eyes? 

18.  How  does  "image  stimulation"  differ  from  light  stimulation  in 
general? 

PRACTICAL   WORK 

To  illustrate  Simple  Properties  of  Light.  —  i .  Heat  an  iron  or 
platinum  wire  in  a  clear  gas  flame.  Observe  that  when  a  high 
temperature  is  reached  it  gives  out  light  or  becomes  luminous. 

2.  Cover  one  hand  with  a  white  and  the  other  with  a  black  piece 
of  cloth,  and  hold  both  for  a  short  time  in  the  direct  rays  of  the  sun. 
Note  and  account  for  the  difference  in  temperature  which  is  felt. 


39°  COORDINATION   AND   SENSATION 

3.  Stand  a  book  or  a  block  of  wood  by  the  side  of  an  empty  pan  in 
the  sunlight,  so  that  the  end  of  the  shadow  falls  on  the  bottom  of  the 
pan.     Mark  the  place  where  the  shadow  terminates  and  fill  the  pan  with 
water.     Account  for  the  shadow's  becoming  shorter. 

4.  Place  a  coin  in  the  center  of  an  empty  pan  and  let  the  members 
of  the  class  stand  where  the  coin  is  barely  out  of  sight  over  the  edges 
of  the  pan.     Fill  the  pan  with  water  and  account  for  the  coin's  coming 
into  view.     Show  by  a  drawing  how  light,  in  passing  from  the  water 
into  the  air,  is  so  bent  as  to  enter  the  eye. 

5.  With  a  convex  lens,  in  a  darkened  room,  focus  the  light  from  a 
candle  flame  so  that  it  falls  on  a  white  screen  and  forms  an  image  of 
the  candle.     Observe  that  the  image  is  inverted.      In  a  well-lighted 
room  focus  the  light  from  a  window  upon  a  white  screen.     Show  that, 
as  the  distance  from  the  window  to  the  screen  is  changed,  the  position 
of  the  lens  must  also  be  changed.     (Accommodation.) 

6.  Hold  a  piece  of  cardboard,  about  eight  inches  square  and  having 
a  smooth,  round  hole  an  eighth  of  an  inch  in  diameter  in  the  center,  in 
front  of  a  lighted  candle  in  a  darkened  room.     Back  of  the  opening 
place  a  muslin  or  paper  screen  (Fig.  157).     Observe  that  a  dim  image 
is  formed.     Account   for  the  fact  that  it  is  inverted.      Hold   a   lens 
between    the    cardboard    and    the    screen    so    that    the    light    passes 
through  it  also.     The   image   should   now  appear  smaller  and   more 
distinct. 

To  prove  the  Presence  of  the  Blind  Spot.  —  Close  the  left  eye  and 
with  the  right  gaze  steadily  at  the  spot  on  the  left  side  of  this  page 


FIG.  1 66.  — Diagram  for  proving  presence  of  the  blind  spot. 

(Fig.  166).  Then  starting  with  the  book  a  foot  or  more  from  the  face, 
move  it  slowly  toward  the  eye.  A  place  will  be  found  where  the  spot  on 
the  right  entirely  disappears.  On  bringing  it  nearer,  however,  it  is  again 
seen.  As  the  book  is  moved  forward  or  backward,  the  position  of  the 


THE   EYE 


391 


image  of  this  spot  changes  on  the  retina.     When  the  spot  cannot  be 
seen,  it  is  because  the  image  falls  on  the  blind  spot. 

Dissection  of  the  Eyeball.  —  Procure  from  the  butcher  two  or  three 
eyeballs  obtained  from  cattle.  After  separating  the  fat,  connective 
tissue,  and  muscle,  place  them  in  a  shallow  vessel  and  cover  with  water. 
Insert  the  blade  of  a  pair  of  sharp  scissors  at  the  junction  of  the  scle- 
rotic coat  with  the  cornea 
and  cut  from  this  point 
nearly  around  the  entire 
circumference  of  the  eye- 
ball, passing  near  the  op- 
tic nerve.  Spread  open 
in  the  water  and  identify 
the  different  parts  from 
the  description  in  the  text. 
Open  the  second  eyeball 

in  water  by  cutting  away 

_         .  FIG.    167.  — Model   for   demonstrating   the 

the  cornea.     Examine  the 

eyeball, 
parts  in  front  of  the  lens. 

To  illustrate  Accommodation.  —  Paste  together  the  ends  of  a  strip  of 
stiff  writing  paper  (two  by  five  inches)  making  a  ring  a  little  less  than 
three  inches  in  diameter.  This  is  to  represent  the  crystalline  lens. 
Now  paste  a  piece  of  thin  paper  (two  by  seven  inches)  upon  a  second 
strip  of  the  same  size,  leaving  an  open  place  in  the  middle  for  the  in- 
sertion of  the  paper  lens.  A  flexible  piece  of  cardboard  (three  by  twelve 
inches)  is  now  bent  into  the  form  of  a  half  circle  and  to  its  ends  are 
fastened  the  strips  of  paper  containing  the  ring.  Make  a  small  hole  in 
each  of  the  four  corners  of  the  bent  cardboard.  Through  these  holes 
pass  two  loops  of  thread,  or  fine  string,  in  opposite  directions,  letting 
the  ends  hang  loose  from  the  cardboard. 

When  everything  is  in  position,  the  tension  from  the  cardboard 
flattens  the  paper  lens,  while  pulling  the  strings  releases  this  tension 
and  permits  the  lens  to  become  more  rounded.  With  this  simple 
device  the  changes  in  the  curvature  of  the  lens  for  near  and  distant 
vision  are  easily  shown. 


CHAPTER   XXIII 
THE  GENERAL  PROBLEM  OF  KEEPING  WELL 

"To  cure  was  the  voice  of  the  Past :  to  prevent  is  the  divine  whispering  of 
To-day." 

As  stated  in  the  introduction  to  our  study,  the  funda- 
mental law  of  hygiene  is  the  law  of  harmony :  Habits  of 
living  must  harmonize  with  the  plan  of  the  body.  Having 
acquainted  ourselves  with  the  plan  of  the  body,  we  may 
now  review  briefly  those  conditions  that  help  or  hinder  its 
various  activities.  The  hygiene  already  presented  in  con- 
nection with  the  study  of  the  various  organs  may  be  con- 
densed into  general  rules,  or  laws,  as  follows : 

1.  Of  exercise:  Exercise  daily  the  important  groups  of 
muscles. 

2.  Of  form :  Preserve  the  natural  form  of  the  body. 

3.  Of   energy:    Observe   regular    periods    of   rest   and 
exercise  and  avoid  exhaustion. 

4.  Of  nutriment:  Eat  moderately  of  a  well-cooked  and 
well-balanced  diet  and  drink  freely  of  pure  water. 

5.  Of  respiration:  Breathe  freely  and  deeply  of   pure 
air  and  spend  a  part  of  each  day  out  of  doors. 

6.  Of   nervous    poise:    Suppress  wasteful   and   useless 
forms  of  nervous  activity,  avoid  nervous  strain,  and  prac- 
tice cheerfulness. 

7.  Of  cleanliness:    Keep  the  body  and  its  immediate 
surroundings  clean. 

8.  Of  restraint:    Abstain  from  the  unnecessary  use  of 

392 


THE   GENERAL  PROBLEM   OF   KEEPING  WELL    393 

drugs  as  well  as  from  the  practice  of  any  form  of  activity 
known  to  be  harmful  to  the  body. 

9.  Of  elimination:  Observe  all  the  conditions  that 
favor  the  regular  discharge  of  waste  materials  from  the 
body. 

Obedience  to  these  laws  is  of  vast  importance  in  the 
proper  management  of  the  body.  They  should,  indeed, 
be  so  thoroughly  impressed  upon  the  mind  as  to  become 
fixed  habits.  There  are,  however,  other  conditions  that 
relate  to  this  problem,  and  it  is  to  these  that  we  now  turn. 
These  conditions  have  reference  more  specifically  to 

The  Prevention  of  Disease.  — While  the  average  length  of 
life  is  not  far  from  thirty-five  years,  the  length  of  time  which 
the  average  individual  is  capable  of  living  is,  according  to 
some  of  the  lowest  estimates,  not  less  than  seventy  years. 
This  difference  is  due  to  disease.  People  do  not,  as  a  rule, 
die  on  account  of  the  wearing  out  of  the  body  as  seen  in 
extreme  old  age,  but  on  account  of  the  various  ills  to 
which  flesh  is  heir.  It  is  true  that  many  people  meet 
death  by  accident  and  not  a  few  are  killed  in  wars,  but 
these  numbers  are  small  in  comparison  with  those  that 
die  of  bodily  disorders.  The  prevention  of  disease  is  the 
greatest  of  all  human  problems.  Though  the  fighting  of 
disease  is  left  largely  to  the  physician,  much  is  to  be 
gained  through  a  more  general  knowledge  of  its  causes 
and  the  methods  of  its  prevention. 

Causes  of  Disease.  —  Disease,  which  is  some  derangement 
of  the  vital  functions,  may  be  due  to  a  variety  of  causes. 
Some  of  these  causes,  such  as  hereditary  defects,  are  re- 
mote and  beyond  the  control  of  the  individual.  Others 
are  the  result  of  negligence  in  the  observance  of  well- 
recognized  hygienic  laws.  Others  still  are  of  the  nature 
of  influences,  such  as  climate,  the  house  in  which  one 


394  PRACTICAL   HYGIENE 

lives,  or  one's  method  of  gaining  a  livelihood,  that  produce 
changes  in  the  body,  imperceptible  at  the  time,  but,  in  the 
long  run,  laying  the  foundations  of  disease.  And  last, 
and  most  potent,  are  the  minute  living  organisms,  called 
microbes  or  germs,  that  find  their  way  into  the  body. 
Although  there  are  two  general  kinds  of  germs,  known  as 
bacteria  (one-celled  plants)  and  protozoa  (one-celled  ani- 
mals), most  of  our  germ  diseases  are  caused  by  bacteria. 

Effects  of  Germs.  — While  there  are  many  kinds  of  germs 
that  have  no  ill  effect  upon  the  body  and  others  that  are 
thought  to  aid  it  in  its  work,  there  are  many  well-known 
varieties  that  produce  effects  decidedly  harmful.  They 
gain  an  entrance  through  the  lungs,  food  canal,  or  skin, 
and,  living  upon  the  fluids  and  tissues,  multiply  with  great 
rapidity  until  they  permeate  the  entire  body.  Not  only  do 
they  destroy  the  protoplasm,  but  they  form  waste  products, 
called  toxins,  which  act  as  poisons.  Diseases  caused  by 
germs  are  known  as  infectious,  or  contagious,  diseases.1 
The  list  is  a  long  one  and  includes  smallpox,  measles, 
diphtheria,  scarlet  fever,  typhoid  fever,  tuberculosis,  la 
grippe,  malaria,  yellow  fever,  and  others  of  common  oc- 
currence. In  addition  to  the  diseases  that  are  well  pro- 
nounced, it  is  probable  that  germs  are  responsible  also  for 
certain  bodily  ailments  of  a  milder  character.2 

1  "  An  infectious  disease  is  one  in  which  disease  germs  infect  (that  is,  invade) 
the  body  from  without.     Among  the  infectious  diseases  are  some  that  are  quite 
directly  and  quickly  conveyed  from  person  to  person  and  to  these  the  term  conta- 
gious is  applied.     Formerly  a  sharp  line  was  drawn  between  infection  and  conta- 
gion, but  to-day  it  is  recognized  that  no  such  line  exists."  —  HOUGH   AND   SEDG- 
WICK,  The  Elements  of  Hygiene  and  Sanitation. 

2  The  arctic  explorer,  Nansen,  states  that  during  all  the  time  that  his  party  was 
exposed  to  the  low  temperature  of  the  arctic  region,  no  one  was  attacked  by  a  cold, 
but  on  returning  to  a  warmer  climate  they  were  subject  to  colds  as  usual.    The 
difference   he  attributes   to   the  absence  of  germs   in  the  severe   arctic  climate. 
There  seems  to  be  no  doubt  but  that  most  of  our  common  colds  are  due  to  attacks 
of  germs. 


THE   GENERAL  PROBLEM   OF   KEEPING  WELL    395 

Avoidance  of  Germ  Diseases.  —  The  problem  of  prevent- 
ing diseases  caused  by  germs  is  an  exceedingly  difficult 
one  and  no  solution  for  all  diseases  has  yet  been  found. 
One's  chances  of  avoiding  such  diseases,  however,  may  be 
greatly  enhanced : 

1.  By  strengthening  the  body  through  hygienic  living  so 
that  it  offers  greater  resistance  to  the  invasions  of  germs. 

2.  By  living  as  far  as  possible  under  conditions  that  are 
unfavorable  to  germ  life. 

3.  By  understanding  the  agencies  through  which  disease 
germs  are  spread  from  person  to  person. 

Conditions  Favorable  and  Unfavorable  for  Germs.  —  Con- 
ditions favorable  for  germ  life  are  supplied  by  animal  and 
vegetable  matter,  moisture,  and  a  moderate  degree  ot 
warmth.  Hence  disease  germs  may  be  kept  alive  in  damp 
cellars  and  places  of  filth.  Even  living  rooms  that  are 
poorly  lighted  or  ventilated  may  harbor  them.  Water 
may,  if  it  contain  a  small  per  cent  of  organic  matter,  sup- 
port such  dangerous  germs  as  those  of  typhoid  fever. 
Fresh  air,  sunlight,  dryness,  cleanliness,  and  a  high  temper- 
ature, on  the  other  hand,  are  destructive  of  germs.  The 
germs  in  impure  water,  as  already  noted  (page  165),  are 
destroyed  by  boiling. 

How  Germs  are  Spread.  —  Some  of  the  more  common 
methods  by  which  the  germs  of  disease  are  spread,  and  by 
so  doing  find  new  victims,  are  as  follows : 

1.  By   Means   of  Foods.  —  Foods,    on    account   of   the 
locality  in  which  they  are   produced   or  the   method  of 
gathering  or  of  handling  them,  may  become  contaminated 
with  germs,  which  are  then  transported  with  the  foods  to 
the  consumer. 

2.  By   Means   of   Dust.  —  Material   containing   germs, 
e.g.,  discharges  from  the  throat  and  lungs,  will  on  drying 


396  PRACTICAL   HYGIENE 

form  dust.  This  is  lifted  with  other  fine  particles  by  the 
air  and  may  be  carried  quite  a  distance.  The  dust  from 
public  halls  and  other  places  where  people  congregate  is 
the  kind  most  likely  to  contain  disease  germs.  Dust  should 
be  breathed  as  little  as  possible  and  only  through  the 
nostrils.  Where  one  is  compelled,  as  in  sweeping,  to 
breathe  dust-laden  air  for  some  time,  he  should  inhale 
through  a  moistened  sponge,  or  cloth,  tied  in  front  of 
the  nostrils. 

3.  By  Means  of  Domestic  Pets  and  Different  Kinds  of 
Household  Vermin.  —  Germs  sticking  to  the  bodies  of 
small  animals  are  carried  about  and  may  be  easily  com- 
municated to  people.  By  this  means,  rats,  mice,  bedbugs, 
etc.,  where  such  exist,  are  frequently  the  means  of  spread- 
ing disease ;  and  particularly  dangerous,  on  this  account,  is 
the  common  house  fly.  Feeding  as  it  does  on  filth  of  all 
kinds,  it  is  easy  for  it  to  transfer  the  bacteria  that  may 
stick  to  its  body  to  the  food  which  is  supplied  to  the  table. 
The  proper  screening  of  houses  and  the  destruction  of 
material  in  which  flies  may  develop,  such  as  the  refuse 
from  stables,  are  necessary  precautions. 

Germs  are  spread  also  by  the  clothing  of  people,  by  rail- 
road and  steamship  lines,  by  the  mails,  and  by  the  natural 
elements.  In  fact,  any  kind  of  carrier,  in  or  upon  which 
germs  can  live,  may  serve  as  a  means  of  spreading  those 
of  certain  kinds. 

Public  Sanitation.  —  The  general  conditions  under  which 
germs  may  thrive  and  some  of  the  means  by  which  they 
are  scattered,  emphasize  the  practical  value  of  measures 
which  have  for  their  purpose  the  making  of  one's  surround- 
ings more  wholesome  and  hygienic.  Such  measures  may 
be  directed  both  toward  one's  immediate  surroundings  — 
the  home  —  and  toward  the  neighborhood,  town,  or  city  in 


THE   GENERAL   PROBLEM    OF   KEEPING   WELL    397 

which  one  lives.      The   hygienic    conditions   of   primary 
importance  in  every  city  or  town  are  as  follows : 

1.  An  adequate  public  supply  of  pure  water. 

2.  An  efficient  system  of  underground  pipes  for  the  re- 
moval of  sewage. 

3.  An  efficient  system  for  removing  from  the  streets 
and  alleys  everything  of  the  nature  of  waste. 

4.  Prevention,  by  enforcement  of  ordinances,  of  spitting 
upon  sidewalks  and  the  floors  of  public  halls  and  convey- 
ances. 

5.  A  hospital  or  sanitarium  in  which  people  can  be  cared 
for  when  sick  with  infectious  diseases. 

In  the  larger  cities  other  hygienic  measures  demand 
attention,  such  as  provisions  for  parks  and  playgrounds, 
the  proper  housing  of  the  poor  of  the  city,  and  the  suppres- 
sion of  the  smoke  and  dust  nuisances.  Crowded  together 
as  people  are  in  the  cities,  the  welfare  of  each  individual 
depends  in  a  large  measure  upon  the  welfare  of  all.  Hence 
the  problems  of  public  sanitation  are  matters  in  which  all 
are  vitally  concerned. 

Sanitary  Conditions  of  the  Home.  —  The  home,  being  the 
feeding  and  resting  place  for  the  entire  family,  is  the 
most  important  factor  in  one's  physical,  as  well  as  moral, 
environment.  For  this  reason  there  is  no  place  where 
careful  attention  to  hygienic  requirements  will  yield  better 
results.  Much  of  the  danger  from  germs  may  be  prevented 
by  instituting  and  maintaining  proper  sanitary  conditions 
in  and  about  the  home. 

One  of  the  first  requisites  of  the  home  is  a  suitable  loca- 
tion for  the  house.  The  house  should  be  built  upon 
ground  that  is  well  drained,  and  if  natural  drainage  be 
lacking,  artificial  drainage  must  be  supplied.  It  should 
not  be  situated  nearer  than  a  quarter  of  a  mile  to  any 


398  PRACTICAL   HYGIENE 

marsh  or  swamp  and,  if  so  near  as  that,  it  ought  to  be  on 
the  side  from  which  the  wind  usually  blows.  A  stone 
foundation  should  be  provided,  and  at  least  eighteen 
inches  of  ventilated  air  space  should  be  left  between  the 
ground  and  the  floor.  Ample  provisions  must  be  made 
for  pure  air  and  sunlight  in  all  the  rooms.  The  cellar,  if 
one  is  desired,  needs  to  be  constructed  with  special  care. 
It  should  be  perfectly  dry  and  provided  with  windows  for 
light  and  ventilation.  Adequate  means  must  also  be  pro- 
vided, by  sewage  pipes  and  other  methods,  for  the  disposal 
of  all  waste.  Where  drainage  pipes  are  provided,  care  must 
be  taken  to  prevent  the  entrance  of  sewer  gas  into  the  house 
and  also  the  passage  of  material  from  these  pipes  into  the 
water  supply.  The  placing  and  connecting  of  sewer  pipes 
should,  of  course,  be  under  the  direction  of  a  plumber. 

The  Water  Supply.  —  Since  water  readily  takes  up  and 
holds  the  impurities  with  which  it  comes  in  contact,  it 
should  be  exposed  as  little  as  possible  in  the  process  of 
collecting.  Where  cistern  water  is 
used,  care  must  be  taken  to  prevent 
filth  from  the  roof  (Fig.  168),  water 
pipes,  or  soil  from  getting  into  the 
reservoir.  Water  should  be  collected 
from  the  roof  only  after  it  has  rained 
long  enough  for  the  roof  and  pipes 
to  have  been  thoroughly  cleaned. 
FIG.  i68.-Contamina-  The  dstern  should  have  no  leaks 
tion  of  cistern  water  by  , 
birds  nesting  in  the  gutter  (Fl&-  l69>'  and  the  tOP  sh°uld  be 

trough.  tightly  closed  to  prevent  the  entrance 

of  small  animals  and  rubbish. 

Shallow  wells  are  to  be  condemned,  as  a  rule,  because  of 
the  likelihood  of  surface  drainage  (Fig.  169),  and  water 
from  springs  should,  for  the  same  reason,  be  used  with 


THE   GENERAL  PROBLEM   OF   KEEPING  WELL 


399 


caution.  Deep  wells  that  are  kept  clean  usually  may  be 
relied  on  to  furnish  water  free  from  organic  impurities, 
but  such  water  often  holds  in  solution  so  much  of  mineral 
impurities  as  to  render  it  unfit  for  drinking.  The  presence 


FIG.  169.  —  Sources  of  contamination  of  cistern  and  well  water. 

Illustration  shows  liability  of  contamination  from  surface 

drainage  and  from  entrance  of  filth  at  top. 

in  water  of  any  considerable  quantity  of  the  compounds  of 
iron  or  calcium  makes  it  objectionable  for  regular  use. 

Hygienic  Housekeeping.  —  However  carefully  a  house 
has  been  constructed  from  a  sanitary  standpoint,  the 
constant  care  of  an  intelligent  housekeeper  is  required 
to  keep  it  a  healthful  place  in  which  to  live.  Daily  clean- 
ing and  airing  of  all  living  rooms  are  necessary,  while  such 
places  as  the  kitchen,  the  cellar,  and"  the  closets  need  extra 
thoughtfulness  and,  at  times,  hard  work.  Moreover,  the 
problem  is  not  all  indoors.  The  immediate  premises  must 
be  kept  clean  and  sightly,  and  all  decaying  vegetable  and 
animal  matter  should  be  removed.  Home  sanitation  con- 


400  PRACTICAL   HYGIENE 

sists,  not  of  one,  but  of  many,  problems,  all  more  or  less 
complex.  None  of  these  can  be  slighted  or  turned  over 
to  a  novice. 

Destruction  of  Infectious  Material.  —  At  times  the  house- 
keeping has  to  be  directed  especially  toward  hygienic  re- 
quirements, such  an  occasion  being  the  sickness  of  one  of 
the  inmates  with  some  contagious  disease.  Unless  special 
precautions  are  taken,  the  disease  will  spread  to  other 
members  of  the  household  and  may  reach  people  in  the 
neighborhood.  Not  only  must  great  care  be  exercised 
that  nothing  used  in  connection  with  the  sick  shall  serve 
as  a  carrier  of  disease,  but  germs  passing  from  the  patient 
should,  as  far  as  possible,  be  actually  destroyed.  All  dis- 
charges from  the  body  likely  to  contain  bacteria  should 
be  burned  or  treated  with  disinfectants  and  buried  deeply 
at  a  remote  distance  from  the  water  supply  to  the 
house. 

After  recovery  all  clothing,  bedding,  and  furniture  used 
in  connection  with  the  sick  should  be  disinfected  or 
burned.  The  room  also  in  which  the  sick  was  cared  for 
should  be  thoroughly  disinfected  and  cleaned ;  in  some 
instances  the  woodwork  ought  to  be  repainted  and  the 
walls  repapered  or  calcimined.  The  purpose  is,  of  course, 
to  destroy  all  germs  and  prevent,  by  this  means,  a  recur- 
rence of  the  disease. 

Fumigation.  —  To  destroy  germs  in  the  air  or  adhering  to  the  walls 
of  rooms,  furniture,  clothing,  etc.,  fumigation  is  employed.  This  is 
accomplished  by  saturating  the  air  of  rooms  with  some  vapor  or  gas 
which  will  destroy  the  germs.  Fumigation  is  quite  generally  employed 
in  the  general  cleaning  after  the  patient  leaves  his  room.  This,  to 
be  effective,  must  be  thorough.  Formaldehyde  is  considered  the  best 
disinfectant  for  this  purpose,  and  it  should  be  evaporated  with  heat  in 
the  proportion  of  one  half  pint  of  the  40  per  cent  solution  to  1000 
cu.  ft.  of  space.  Since  formaldehyde  is  inflammable  and  easily  boils 


THE   GENERAL   PROBLEM    OF    KEEPING    WELL    401 

over,  it  has  to  be  evaporated  with  care.  It  should  be  boiled  in  a  tall 
vessel  (a  tin  or  copper  vessel  which  holds  about  four  times  the  quantity 
to  be  evaporated)  over  a  quick  fire,  the  room  being  tightly  closed 
(openings  around  windows  and  doors  plugged  with  cotton  or  cloth). 
After  three  or  four  hours  the  room  may  be  opened  and  thoroughly 
aired.  Since  formaldehyde  is  most  disagreeable  to  breathe,  one  should 
not  attempt  to  occupy  the  room  until  it  is  free  from  the  gas.  This  will 
require  a  day  or  more  of  thorough  ventilation. 

Facts  Relating  to  the  Spread  of  Certain  Diseases.  —  The 
problem  of  preventing  disease  in  general  often  resolves 
itself  into  the  problem  of  preventing  the  spread  of  some 
particular  disease.  It  is  then  of  vital  importance  to  know 
the  special  method  by  which  the  germs  of  this  disease  leave 
the  body  of  the  patient  and  are  conveyed  to  the  bodies  of 
others.  Some  of  these  methods  are  novel  in  the  extreme, 
and  are  not  at  all  in  accord  with  prevailing  notions.  Par- 
ticularly is  this  true  of  that  disease  known  as 

Malaria,  or  Malarial  Fever. — This  disease,  so  common 
in  warm  climates  and  also  prevalent  to  a  large  extent  in 
the  temperate  zones,  is  due  to  animal  germs  (protozoa), 
which  attack  and  destroy  the  red  corpuscles  of  the  blood. 
These  germs,  it  is  found,  pass  from  malarial  patients  to 
others  through  the  agency  of  a  variety  of  mosquitoes 
known  as  Anopheles.  In  sucking  the  blood  of  a  malarial 
patient,  the  mosquito  first  infects  her  own  body.1  In  the 
body  of  the  mosquito  the  germs  undergo  an  essential 
stage  of  their  development,  after  which  they  are  injected 
beneath  the  skin  of  whomsoever  the  mosquito  feeds 
upon.  For  the  spreading  of  malaria,  then,  two  conditions 
are  necessary  :  first,  there  must  be  people  who  have  the 
disease;  and  second,  there  must  be  in  the  neighborhood 
the  special  variety  of  mosquito  that  spreads  the  disease. 

i  An  interesting  biological  fact  is  that  the  female  Anopheles,  and  not  the  male, 
sucks  the  blood  of  animals  and  is  the  cause  of  the  spreading  of  malaria. 


402 


PRACTICAL   HYGIENE 


If  either  condition  be  lacking,  the  disease  is  not  spread. 
The  malarial  mosquito  {Anopheles}  may  be  distinguished 
from  the  harmless,  variety  (Culex)  by  the  position  which 
it  assumes  in  resting,  as  shown  in  Fig.  I/O. 


FIG.  170.  —  Mosquitoes  in  resting  position.  (From  Howard's  Mosquitoes?) 
On  left  the  malarial  mosquito  {Anopheles} ;  on  the  right  the  harmless  mosquito 
{Culex). 

Remedies  against  Mosquitoes.  —  The  natural  method  of 
preventing  the  spread  of  malaria  is,  of  course,  the  destruc- 
tion of  mosquitoes.  This  'is  accomplished  by  draining 
pools  of  water  where  they  are  likely  to  breed,  and  by  cov- 
ering pools  of  water  that  cannot  be  drained  with  crude 
petroleum  or  kerosene.  The  kerosene,  by  destroying  the 

larvae,  prevents  the  development 
of  the  young.  In  communities 
where  such  measures  have  been 
diligently  carried  out,  the  mos- 
quito pest  has  been  practically 
eliminated.  Other  methods  are 
also  under  investigation,  such  as 
the  stocking  of  shallow  bodies  of 
water  with  varieties  of  fish  that 

feed  upon  the  mosquito  larvae. 
FIG.  171.  — Stegomyia,  T-,- 

the     yellow -fever      mosquito          Yell°W     Fever.-    This     scourge 

(after  Howard).  of    the    tropics    is,    like   malaria, 


THE   GENERAL  PROBLEM   OF   KEEPING   WELL    403 

caused  by  animal  germs.  It  is  also  propagated  in  the 
same  manner  as  malaria,  but  by  a  different  variety  of 
mosquito  (Stegomyia,  Fig.  171).  The  stamping  out  of 
yellow  fever  in  Havana,  the  Panama  Canal  Zone,  and 
other  places,  through  the  destruction  of  this  variety  of 
mosquito,  affords  ample  proof  of  the  correctness  of  the 
"  mosquito  theory." 

Consumption,  or  tuberculosis  of  the  lungs,  spoken  of  as 
the  "  white  plague,"  was  among  the  first  diseases  shown 
to  be  due  to  bacteria.  Consumption  is  now  recognized  as 
an  infectious  disease,  though  not  so  readily  communicated 


FIG.  172.  — Consumption  germs  from  the  spit  of  one  having  the  disease. 
Highly  magnified  and  stained.  (Huber's  Consumption  and  Civilization.} 

as  some  other  diseases.  Several  methods  are  recognized 
by  which  the  germs  are  passed  from  the  sick  to  the  well, 
the  most  important  being  as  follows : 

1.  By  personal  contact  of  the  sick  with  the  well,  espe- 
cially in  kissing. 

2.  By  the  sputum,  or  spit,  which,  if  allowed  to  dry,  is 
blown  about  as  dust  and  breathed  into  the  lungs 1  (Fig.  172). 

3.  By  means  of  objects  (drinking  cups,  tableware,  etc.) 
that  have  been  handled  by  consumptives. 

1  The  habit  of  spitting  upon  the  floors  of  public  buildings  and  street  cars,  and 
also  upon  sidewalks,  is  now  recognized  as  a  most  dangerous  practice.  Not  only 
consumptives,  but  people  with  throat  affections,  may  do  no  end  of  harm  in  the 
spreading  of  disease  by  carelessness  in  this  respect. 


404  PRACTICAL  HYGIENE 

4.  By  infectious  material  associated  with  houses  or 
rooms  in  which  consumptives  have  lived. 

These  methods  of  spreading  consumption  suggest  the 
necessity  for  the  greatest  care,  on  the  part  of  both  the 
patient  and  those  having  him  in  charge.1  The  material 
coughed  up  from  the  lungs  and  throat  should  be  collected 
on  cloths  or  paper  handkerchiefs  and  afterwards  burned. 
The  house  where  a  consumptive  has  lived  should  be  dis- 
infected, repapered  or  calcimined,  and  thoroughly  cleaned 
before  it  is  again  occupied.  The"  inside  woodwork  should 
also  be  repainted.  The  approaches  to  the  house  where 
the  patient  may  have  expectorated  should  be  disinfected 
and  cleaned.  Since  the  germs  are  able  to  live  in  the  soil, 
fresh  lime  or  wood  ashes  should  be  spread  around  the 
doorsteps  and  along  the  walks. 

Typhoid  Fever,  one  of  our  most  dangerous  diseases,  is 
caused  by  germs  (bacteria)  that  enter  the  body  through 
the  food  canal.  They  attack  certain  glands  in  the  walls 
of  the  small  intestine,  where  they  produce  toxins  that  pass 
with  the  germs  to  all  parts  of  the  body.  Typhoid  fever 
germs  spread  from  those  having  the  disease  to  others, 
chiefly  through  the  discharges  from  the  bowels  and  the 
kidneys.  The  germs  contained  in  these,  if  not  destroyed 
by  disinfectants,  find  their  way  into  the  soil,  or  into  sewage, 
where  they  may  be  picked  up  by  water  and  widely  dis- 
tributed. Finding  suitable  places,  such  as  those  containing 
decaying  material,  the  germs  may  rapidly  increase  in  num- 
ber, and  from  these  sources  find  their  way  into  the  bodies  of 
new  victims.  They  are  likely,  on  account  of  manures,  to 
get  on  vegetables  ;  on  account  of  uncleanly  methods  of  milk- 
ing, to  get  into  the  milk  supply;  and  from  sewerage  out- 

1  For  further  information  on  the  care  of  consumptives,  consult  Huber's  Con- 
sumption and  Civilization. 


THE   GENERAL   PROBLEM   OF   KEEPING   WELL    405 

lets,  to  get  into  the  oysters  that  grow  in.  bays  and  harbors 
near  seaboard  cities ;  but  they  are  most  frequently  intro- 
duced into  the  body  through  the  drinking  of  impure  water. 

Diphtheria,  also  known  as  "  membranous  croup,"  is 
caused  by  germs  that  attack  the  membranes  of  the  throat. 
This  most  dangerous  of  children's  diseases  is  spread  chiefly 
by  discharges  from  the  mouth  and  throat  These  should 
be  collected  on  cloths  and  burned,  or  rendered  harmless 
with  disinfectants.  The  disease  may  be  spread  also  by 
objects  brought  into  contact  with  the  mouth,  such  as  cups, 
toys,  pencils,  etc.  Children  are  known  to  have  diph- 
theria germs  in  the  mouth  for  some  time  after  recovering 
from  the  disease,  and  should,  for  this  reason,  be  kept  away 
from  other  children  until  pronounced  safe  by  the  physician. 

The  antitoxin  metJiod  of  treating  diphtheria  has  robbed 
this  disease  of  much  of  its  terror,  yet  it  not  infrequently 
happens  that  the  physician  is  called  too  late  to  administer 
this  remedy  to  the  best  advantage.  Since  certain  cases  of 
diphtheria  are  likely  to  be  mistaken  for  croup,  the  parent 
frequently  does  not  realize  the  serious  condition  of  the 
child.  A  croupy  cough  that  lasts  through  the  day,  or  a 
sore  throat  which  shows  small  white  patches,  are  indica- 
tions of  diphtheria. 

Scarlet  Fever,  Measles,  Chicken  Pox,  and  Smallpox,  on 
account  of  the  eruptions  of  the  skin  which  attend  them, 
are  classed  as  eruptive  diseases.  As  the  eruptions  heal, 
scales  separate  from  the  skin,  and  these  are  supposed  to  be 
the  chief  means  of  spreading  the  germs.  Attention  must 
be  given  to  the  destruction  of  these  scales  by  burning  or 
thoroughly  disinfecting  all  objects,  such  as  clothing,  bed- 
ding, etc.,  that  may  serve  as  carriers  of  them.  Those  having 
eruptive  diseases  should  be  confined  to  their  rooms  as  long 
as  the  scales  continue  to  separate  from  the  body. 


406  PRACTICAL   HYGIENE 

Vaccination.  —  The  method  of  preventing  smallpox 
known  as  vaccination,  which  has  been  practiced  since  its 
discovery  in  1796  by  Jenner,  has  always  proved  effective. 
In  some  instances  the  sore  arm  causes  considerable  incon- 
venience, but  this  generally  results  from  neglect  to  cleanse 
the  arm  thoroughly  before  applying  the  virus,  or  from  con- 
tact of  the  sore  with  the  clothing  later.  The  virus  should 
be  applied  by  a  physician  and  the  wound  should  be  pro- 
tected after  the  operation.  If  discomfort  is  felt  when  it 
"  takes,"  medical  advice  should  be  sought. 

Isolation,  or  quarantining,  is  a  most  important  method 
of  combating  contagious  diseases.  By  removing  the  sick 
from  the  well  many  outbreaks  of  disease  are  quickly 
checked.  Isolation  of  individual  patients,  and  sometimes 
of  infected  neighborhoods,  is  absolutely  necessary ;  and 
while  this  works  a  hardship  to  the  few,  it  is  frequently 
the  only  safeguard  of  the  many.  The  community,  on  the 
other  hand,  should  make  ample  provision  for  the  care  of 
the  afflicted  in  the  way  of  hospitals,  or  sanitaria,  and  if  it  is 
deemed  necessary  to  remove  people  from  their  homes, 
they  should  not  be  subjected  to  unnecessary  hardship. 

Where  one  is  sick  from  some  contagious  disease  in  the 
home  and  there  is  liability  of  communicating  it  to  the  other 
members  of  the  family,  room  isolation  should  be  practiced. 
Infection  cannot  spread  through  solid  walls,  and  where  the 
doors,  and  the  cracks  around  the  doors,  are  kept  com- 
pletely closed  and  the  usual  precautions  are  observed  by 
those  attending  the  patient,  the  other  inmates  of  the  house 
can  be  protected  from  the  disease. 

The  Physician  and  His  Work.  —  In  combating  disease 
the  services  of  the  physician  are  a  prime  necessity.  The 
special  knowledge  which  he  has  at  his  command  enables 
the  conflict  to  be  carried  on  according  to  scientific  require- 


THE  GENERAL   PROBLEM   OF   KEEPING  WELL    407 

ments  and  vastly  increases  the  chances  for  recovery.  He 
should  be  called  early  and  his  directions  should  be  care- 
fully followed.  Everything,  however,  must  not  be  left  to 
the  physician,  for  recovery  depends  as  much  upon  proper 
nursing  and  feeding  as  upon  the  drugs  that  are  adminis- 
tered. Of  great  importance  is  the  saving  of  the  energy  of 
tJte  patient,  and  to  accomplish  this  visitors  should,  as  a 
rule,  be  excluded  from  the  sick  room. 

Precautions  in  Recovery  from  Disease.  —  Many  diseases, 
if  severe,  not  only  leave  the  body  in  a  weakened  condition, 
but  may,  through  the  toxins  which  the  germs  deposit,  cause 
untold  harm  if  the  patient  leaves  his  bed  or  resumes  his 
usual  activities  too  soon.  Especially  is  this  true  of 
typhoid  fever,1  diphtheria,  scarlet  fever,  and  measles. 
Rheumatism  and  affections  of  the  heart,  lungs,  kidneys, 
and  other  bodily  organs  frequently  follow  these  diseases, 
as  the  result  of  slight  exposure  or  exertion  before  the 
body  has  sufficiently  recovered  from  the  effects  of  the 
toxins.  To  guard  against  such  results,  certain  physicians 
require  their  patients  to  keep  their  beds  for  a  week,  or 
longer,  after  apparent  recovery  from  diseases  like  typhoid 
fever,  diphtheria,  and  scarlet  fever. 

Relation  of  Vocation  to  Disease.  —  With  a  few  excep- 
tions, the  pursuit  of  one's  vocation,  or  calling  in  life,  does 
not  supply  either  the  quantity  or  the  kind  of  activity  that  is 
most  in  harmony  with  the  plan  of  the  body.  Especially 
is  this  true  of  work  that  requires  most  of  the  time  to  be 
spent  indoors,  or  which  exercises  but  a  small  portion  of  the 
body.  The  effect  of  such  vocations,  if  not  counteracted, 

lAs  typhoid  fever  is  a  disease  of  the  small  intestine,  great  care  must  be 
exercised  in  taking  food  and  in  the  bodily  movements.  Solids  greatly  irritate  the 
diseased  lining  of  the  intestine,  and  the  weakened  walls  may  actually  be  broken 
through  by  pressure  resulting  from  moving  about. 


408  PRACTICAL   HYGIENE 

is  to  weaken  certain  organs,  thereby  disturbing  the  func- 
tional equilibrium  of  the  body  —  a  result  that  may  be 
brought  about  either  by  the  overwork  of  particular  organs 
or  by  lack  of  exercise  of  others.  Herein  lies  the  explana- 
tion of  the  observed  fact  that  people  of  the  same  calling  in 
life  have  similar  diseases. 

A  Special  Problem  for  the  Brain  Worker.  —  Farthest 
removed  from  those  forms  of  activity  which  harmonize 
with  the  plan  of  the  body,  and  which  therefore  are  most 
hygienic,  is  that  class  of  workers  known  as  the  profes- 
sional class,  or  the  "brain  workers."  This  class  includes 
not  only  the  members  of  the  learned  professions  —  law, 
medicine,  and  the  ministry — but  a  vast  army  of  business 
men,  engineers,  teachers,  stenographers,  office  clerks,  etc., 
a  class  that  is  ever  increasing  as  our  civilization  advances. 
It  is  this  class  in  particular  that  must  give  attention  to 
those  conditions  that  indirectly,  but  profoundly,  influence 
the  bodily  well-being  and  must  seek  to  obviate  if  possible 
such  weaknesses  as  the  occupation  induces. 

The  Remedy  lies  in  two  directions  —  that  of  spending 
sufficient  time  away  from  one's  work  to  allow  the  body  to 
recover  its  normal  condition,  and  that  of  counteracting  the 
effect  of  the  work  by  special  exercise  or  other  means. 
In  many  cases  the  first  symptoms  of  weakness  indicate  a 
suitable  remedy.  Thus  exhaustion  from  overwork  sug- 
gests rest  and  recreation.  The  diverting  of  too  much 
blood  from  other  parts  of  the  body  to  the  brain  suggests 
some  form  of  exercise  which  will  equalize  the  circulation. 
If  feebleness  of  the  digestive  organs  is  being  induced, 
some  natural  method  of  increasing  the  blood  supply  to 
these  organs  is  to  be  looked  for.  And  effects  arising 
from  lack  of  fresh  air  and  sunlight  are  counteracted  by 
spending  more  time  out  of  doors. 


THE   GENERAL   PROBLEM   OF   KEEPING   WELL    409 

Exercise  as  a  Counteractive  Agent.  —  In  counteracting 
tendencies  to  disease  and  in  the  maintenance  of  the  func- 
tional equilibrium  of  the  body,  no  agent  has  yet  been  dis- 
covered of  greater  importance  than  physical  exercise, 
when  applied  systematically  and  persistently.  This  may 
consist  of  exercises  that  call  into  play  all  the  muscles  of 
the  body,  or  which  are  concentrated  upon  special  parts. 
When  general  tonic  effects  are  desired,  the  exercise  should 
be  well  distributed;  but  when  counteractive  or  remedial 
effects  are  wanted,  it  must  be  applied  chiefly  to  the  parts 
that  are  weak  or  that  have  not  been  called  into  action  by 
the  regular  work.  Unfortunately,  health  is  sometimes 
confused  with  physical  strength  and  exercise  is  directed 
toward  the  stronger  parts  of  the  body  with  the  effect  of 
making  them  still  stronger.  Not  only  is  health  riot  to  be 
measured  by  the  pounds  that  one  can  lift  or  by  some  gym- 
nastic feat  that  one  can  perform,  but  the  possession  of 
great  muscular  power  may,  if  the  heart  and  other  vital 
organs  be  not  proportionally  strong,  prove  a  menace  to 
the  health.  This  being  true,  one  having  his  health  pri- 
marily in  view  will  use  physical  exercise,  in  part  at  least, 
as  a  means  of  building  up  organs  that  are  weak.  Since 
the  body,  like  a  chain,  can  be  no  stronger  than  its  weak- 
est part,  this  is  clearly  the  logical  method  of  fortifying  it 
against  disease. 

Value  of  Work.  —  Although  there  may  exist  in  one's 
vocation  certain  tendencies  to  disease,  it  must  not  be 
inferred  that  work  in  itself  is  detrimental  to  health. 
Health  demands  activity,  and  those  forms  of  activity 
that  provide  a  regular  and  systematic  outlet  for  one's 
surplus  energy  and  compel  the  formation  of  correct 
habits  of  eating,  sleeping,  and  recreating  best  serve  the 
purpose.  Work  furnishes  activity  'of  this  kind  and  serves 


410  PRACTICAL   HYGIENE 

also  as  a  safeguard  against  the  unhealthful  and  immoral 
habits  contracted  so  often  from  idleness.  Even  physical 
exercise  which  has  for  its  purpose  the  reenforcement  of 
the  body  against  disease  may  frequently  consist  of  useful 
work  without  diminishing  its  hygienic  effects. 

The  Mental  Attitude.  —  While  a  proper  thoughtf ulness 
and  care  for  the  body  is  both  desirable  and  necessary,  it 
is  also  true  that  over-anxiety  about,  or  an  unnatural  atten- 
tion to,  the  needs  of  the  body  reacts  unfavorably  upon 
the  nervous  system.  Observance  of  the  laws  of  health, 
therefore,  should  be  natural  and  without  special  effort  —  a 
matter  of  habit.  The  'attention  should  never  be  turned 
with  anxiety  upon  any  organ  or  process,  but  the  mental 
attitude  should  at  all  times  be  that  of  confidence  in  the 
power  of  the  body  organization  to  do  its  work.  Fear  and 
morbidity,  which  are  disturbing  and  paralyzing  factors, 
should  be  supplanted  by  courage,  cheerfulness,  and  hope- 
fulness. 

Let  it  be  borne  in  mind  that  hygienic  living  requires 
nothing  more  than  the  application  of  the  same  intelligence 
and  practical  common  sense  to  the  care  of  the  body  that 
the  skillful  mechanic  applies  to  an  efficient,  but  delicate, 
machine.  And,  just  as  in  the  case  of  the  machine,  care 
of  the  body  keeps  its  efficiency  at  the  maximum  and 
lengthens  the  period  that  it  may  be  used.  This  end  and 
aim  of  hygienic  living  is  best  attained  by  cultivating  that 
attitude  of  mind  toward  the  body  that  avoids  interference 
in  the  vital  processes  and  permits  the  natural  appetites, 
sensations,  and  desires  to  indicate  very  largely  the  body's 
needs. 

Attitude  toward  Habit-forming  Drugs.  —  Among  the  dif- 
ferent substances  introduced  into  the  body,  either  as  foods 
or  as  medicines,  are  a 'number  which  have  the  effect  of 


THE   GENERAL   PROBLEM   OF   KEEPING   WELL      411 

developing  an  artificial  appetite  or  craving  which  leads  to 
their  continued  use.  Since  the  effect  of  such  substances  is 
usually  harmful  and  since  they  tend  to  engraft  themselves 
upon  communities  as  social  customs,  they  present  a  two- 
fold relation  to  the  general  problem  of  keeping  well.  The 
individual  may  be  injured  through  the  personal  use  which 
he  makes  of  them,  or  he  may  be  injured  through  the  effect 
which  they  have  upon  relatives  or  friends  or  upon  society 
at  large.  Since  our  social  environment  is  a  factor  in  health 
little  less  important  than  our  physical  environment,  the 
conditions  that  make  for  their  continuance  should  be  more 
generally  understood. 

How  Social  Agencies  perpetuate  the  Use  of  Habit-forming 
Drugs. —  When  the  use  of  some  habit-forming  drug  has 
risen  to  the  importance  of  a  general  custom,  a  number  of 
conditions  arise  which  tend  to  continue  its  use,  even  though 
the  fact  may  be  quite  generally  known  that  the  substance 
does  harm.  In  the  first  place,  those  who  have  formed  the 
habit  suffer  inconvenience  and  distress  when  deprived  of 
its  use.  In  the  second  place,  a  number  of  people  will  have 
become  interested  in  the  production  and  sale  of  the  sub- 
stance, and  these  will  lose  financially  if  it  is  discontinued. 
In  the  third  place,  those  of  the  rising  generation  will,  from 
imitation  or  persuasion,  be  constantly  acquiring  the  habit 
before  they  are  sufficiently  mature  to  decide  what  is  best 
for  them.  Thus  may  the  use  of  a  substance  most  harmful, 
such  as  the  opium  of  the  Chinese,  be  indefinitely  continued 
—  a  species  of  slavery  from  which  the  individual  finds  it 
hard  to  escape. 

Such  is  human  nature  and  such  are  the  forces  and  influ- 
ences of  human  society,  that  the  freeing  of  a  people  from 
the  bondage  of  some  habit-forming  drug  cannot  be  accom- 
plished without  strenuous  and  persistent  effort.  Education, 


412  PRACTICAL   HYGIENE 

persuasion,  the  good  example  of  abstainers,  and  legal  re- 
strictions must  be  pitted  against  the  forces  that  make  for 
its  continuance.  Such  a  struggle  is  now  in  progress  in  all 
civilized  countries  relative  to  the  use  of  alcoholic  beverages.1 

How  the  Use  of  Alcohol  became  a  Social  Custom.  —  The 
general  use  of  alcohol  as  a  beverage  may  be  accounted  for 
by  three  facts.  Alcohol  is  a  habit-forming  drug ;  it  has  a 
stimulating  effect  which  many  have  found  agreeable ;  and 
being  a  product  of  the  fermentation  of  fruit  juices  and 
other  liquids  containing  sugar,  it  is  easily  obtained. 
Through  the  operation  of  these  causes  the  human  family 
became  habituated  very  early  to  the  use  of  alcohol.  The 
"wine"  of  primitive  man,  however,  did  little  harm  as  com- 
pared with  the  alcoholic  liquors  of  modern  times.  It  was 
a  weak  solution  and  on  account  of  the  crude  methods  of 
manufacture  and  storage  could  only  be  produced  in  limited 
quantities.  Perhaps  the  worst  effect  of  its  early  use  was 
the  establishment  of  a  general  belief  in  its  power  to  benefit, 
since  this  laid  the  foundation  for  excess  in  its  use  when  the 
developments  of  a  later  period  made  it  possible. 

During  the  eleventh  century  the  method  of  making  alco- 
holic drinks  from  starch-producing  substances,  such  as 
wheat,  barley,  and  potatoes,  became  quite  generally  known, 
and  also  the  method  of  concentrating  them  by  distillation. 


1  Alcoholic  beverages  include  all  the  various  kinds  of  drinks  that  owe  their 
stimulating  properties  to  a  substance,  ethyl  alcohol  (C^HsOH),  which  is  made 
from  sugar  by  the  process  of  fermentation.  They  include  malt  liquors,  such  as 
beer  and  ale,  which  contain  from  three  to  eight  per  cent  of  alcohol ;  wines,  such  as 
claret,  hock,  sherry,  and  champagne,  which  contain  from  five  to  twenty  per  cent  of 
alcohol ;  and  distilled  liquors,  such  as  brandy,  whisky,  rum,  and  gin,  which  contain 
from  thirty  to  sixty-five  per  cent  of  alcohol.  Alcoholic  beverages  all  contain  con- 
stituents other  than  alcohol,  these  varying  with  the  materials  from  which  they  are 
made  and  with  the  processes  of  manufacture.  The  distilled  liquors  are  so  called 
from  the  fact  that  their  alcohol  has  been  separated  from  the  fermenting  substances 
by  distillation. 


THE   GENERAL   PROBLEM    OF    KEEPING    WELL      413 

This  knowledge  made  possible  the  manufacture  of  alco- 
holic drinks  in  large  quantities  and  in  considerable  variety. 
Alcoholic  indulgence  was  now  no  longer  the  pastime  of  the 
few,  but  the  privilege  of  all.  Its  evil  effects  followed  as  a 
matter  of  course ;  and  as  these  became  more  and  more  ap- 
parent, there  began  the  struggle  to  restrict  the  consumption 
of  alcohol  which  has  continued  with  varying  success  to  the 
present  time. 

Counts  against  Alcohol.  —  The  statements  found  in  differ, 
ent  parts  of  this  book  relative  to  the  effects  of  alcohol  upon 
the  body  may  here  be  summarized  as  follows :  — 

1.  Alcohol  has  an  injurious  effect  upon  the  white  cor- 
puscles of  the  blood  and  lessens  the  power  of  the  body  to 
resist  attacks  of  disease  (pages  35,  98). 

2.  Alcohol    injures    the    heart   and   the   blood   vessels 
(page  56). 

3.  Alcohol  causes  diseases  of  the  liver  and  kidneys  and 
interferes  with  the  discharge  of  waste  through  these  organs 
(pages  210,  212). 

4.  Alcohol  interferes  seriously  with  the  regulation  of 
the  body  temperature  (page  271). 

5.  Alcohol  is  one  of  the  worst  enemies  to  the  nervous 
system  (pages  326,  332-334,  336,  337). 

6.  Through    its   effect   upon   the  nervous  system  and 
through    its   interference  with   the   production    of   bodily 
energy  (page  195),  alcohol  greatly  diminishes  the  efficiency 
of  the  individual. 

7.  The  taking  of  alcohol  in  amounts  that  apparently  do 
not  harm  the  tissues  is,  nevertheless,  liable  to  produce  a 
habit  which  leads  to  its  use  in  amounts  that  are  decidedly 

harmful. 

Alcohol  and  the  Social  Environment.  —  Our  social  environ- 
ment includes  the  people  with  whom  we  are  directly  or 


414  PRACTICAL   HYGIENE 

indirectly  associated.  The  presence  in  any  community  of 
those  who  are  immoral,  inefficient,  or  defective,  places  a 
burden  upon  those  who  are  mentally  and  physically  capable 
and  renders  them  liable  to  results  which  are  the  outgrowth 
of  weakness  or  viciousness.  The  fact  that  alcohol  causes 
pauperism,  crime,  and  general  inefficiency,  thereby  render- 
ing the  social  environment  less  conducive  to  what  is  best 
in  life,  is  plainly  evident.  To  realize  how  alcohol  harms 
the  individual  through  its  effects  upon  society  in  general, 
one  has  only  to  take  into  account  his  dependence  upon 
society  for  intellectual  and  moral  stimuli,  for  industrial  and 
economic  opportunity,  for  protection,  and  for  general  con- 
ditions that  make  for  health  and  happiness.  As  we  strive 
to  improve  our  physical  environment,  so  should  we  also 
strive  for  the  betterment  of  social  conditions. 

Industrial  Use  of  Alcohol.  —  Interesting  and  instructive  in  this  con- 
nection is  the  fact  that  alcohol  is,  after  all,  a  substance  capable  of  ren- 
dering great  service  to  humanity.  The  injury  which  it  causes  is  the 
result  of  its  misuse.  Though  unfit  for  introduction  into  the  human 
body,  except  in  the  most  guarded  manner,  it  is  adapted  to  a  great  variety 
of  uses  outside  of  the  body.  A  combustible  substance  which  is  readily 
convertible  into  a  gas,  it  may  be  substituted  for  gasoline  in  the  cooking 
of  food,  lighting  of  dwellings,  and  the  running  of  machinery.  As  a 
solvent  for  gums,  resins,  essential  oils,  etc.,  it  is  used  in  the  preparation 
of  varnishes,  extracts,  perfumes,  medicines,  and  numerous  other  sub- 
stances of  everyday  use.  Through  its  chemical  interactions,  it  is  used 
in  the  manufacture  of  ether,  chloroform,  explosives,  collodion,  celluloid, 
dyestuffs,  and  artificial  silk.  In  fact,  alcohol  is  stated  by  one  authority 
to  be,  next  to  water,  the  most  valuable  liquid  known.1 

Opposed  to  an  extensive  use  of  alcohol  for  industrial  purposes  is  the 
guard  which  the  government  must  keep  over  its  manufacture  on  account 
of  its  use  in  beverages.  Though  alcohol  may  be  profitably  manufac- 
tured and  sold  at  thirty  cents  per  gallon,  the  government  revenue  stamp 
of  $2.08  per  gallon  practically  prohibits  its  use  for  many  purposes.  A 
step  toward  a  wider  application  to  industrial  purposes  has  been  taken 
1  Duncan,  The  Chemistry  of  Commerce. 


THE   GENERAL   PROBLEM    OF   KEEPING   WELL     415 

by  the  law  permitting  the  sale  of  so-called  "denatured  "  1  alcohol  with- 
out the  tax  for  revenue.  This  law  has  proved  beneficial  to  some  extent, 
though  the  practical  solution  of  the  problem  is  still  remote. 

Nicotine  and  Social  Custom. —  The  influences  which 
brought  about  a  general  use  of  tobacco  are  similar  to, 
though  not  identical  with,  those  that  engrafted  alcohol 
upon  society.  The  drug  nicotine  is  a  habit-forming  sub- 
stance and  the  plant  producing  it  is  easily  cultivated.2  Its 
immediate  effect  upon  the  user  is  generally  agreeable, 
acting  as  a  stimulant  to  some,  but  having  a  soothing  effect 
upon  the  nerves  of  others.  Moreover,  a  strong  deterring 
factor  in  its  use  is  lacking,  since  its  harmful  effects  are  not 
readily  discernible  and  by  many  are  avoided  through 
moderation  in  its  use. 

As  with  alcohol,  tobaQco  is  conveniently  used  to  promote 
sociability  among  men,  a  fact  which  has  much  to  do  with 
its  very  general  use.  If  it  could  be  limited  to  social  pur- 
poses, it  would  likely  do  little  harm,  but  the  habit,  once 
started,  is  continued  without  reference  to  sociability  —  a 
matter  of  selfish  indulgence.  In  fact,  one  effect  of  tobacco 
is  to  cause  the  user  to  become  less  sensitive  to  the  rights 
of  others,  this  being  evidenced  by  smokers  who  do  not 
hesitate  to  make  rooms  and  public  halls  almost  unbearable 
to  those  unaccustomed  to  tobacco. 

Counts  against  Nicotine.  —  The  physiological  objections 
to  the  use  of  tobacco,  as  already  stated  (pages  56,  92,  326, 
333,  336),  are  the  following:  — 

i.    The   use   of   tobacco   before   one  reaches   maturity 

1  Alcohol  is  "denatured"  by  adding  substances  to  it  such  as  wood  alcohol, 
which  render  its  use  as  a  beverage  impossible. 

2  The  tobacco  plant,  Nicotiana  tobacum,  is  a  native  of  America,  and  the  use  of 
tobacco  began  with  the  American  Indians.     It  was  taken  back  to  Europe  by  the 
early  explorers,  Sir  Walter  Raleigh  being  credited  with  introducing  it  to  the  nobility 
of  England. 


416  PRACTICAL    HYGIENE 

stunts  the  growth.  The  boy  who  uses  it  cannot  develop 
into  so  strong  and  capable  a  man  as  he  would  by  leaving 
it  alone. 

2.  Tobacco  injures  the  heart. 

3.  Tobacco  injures  the  air  passages,  especially  when 
inhalation  is  practiced. 

4.  Tobacco   injures   the   nervous    system    and   by  this 
means  interferes  in  a  general  way  with  the  bodily  processes. 
For  the  same  reason  it  interferes  with  mental  and  moral 
development,  the  cigarette  being  a  chief  cause  of  criminal 
tendencies  in  boys. 

5.  In  some  cases  tobacco  injures  the  vision. 

6.  The  tobacco  habit  is  expensive  and  is  productive  of 
no  good  results. 

Tobacco  and  the  Rising  Generation.  —  The  problem  of 
limiting  the  use  of  tobacco  to  the  point  where  it  would  do 
slight  harm,  in  comparison  to  what  it  now  does,  would  be 
solved  if  those  under  twenty  years  of  age  could  be  kept 
from  using  it.  But  few  would  then  acquire  the  habit,  and 
those  who  did  would  not  be  so  seriously  injured.  In  our 
own  country  it  lies  within  the  province  of  the  home  and 
the  school  to  bring  about  this  result.  The  fact  that  par- 
ents use  tobacco  is  no  reason  why  the  boys  should 
also  indulge.  The  decided  difference  in  effects  upon  the 
young  and  upon  the  mature  makes  this  point  very  clear. 
Laws  protecting  boys  from  the  evil  effects  of  tobacco,  not 
only  cigarettes,  but  other  forms  as  well,  are  both  just  and 
necessary. 

Social  Custom  and  the  Caffeine  Habit.  —  By  suitable  pro- 
cesses a  white,  crystalline  solid,  easily  soluble  in  water,  can 
be  separated  from  the  leaves  of  tea,  and  from  the  berry  of 
the  coffee  plant.  This  is  the  drug  caffeine,  the  substance 
which  gives  to  tea  and  coffee  their  stimulating  properties, 


THE   GENERAL   PROBLEM   OF   KEEPING   WELL     417 

but  not  their  agreeable  flavors.  Less  injurious,  on  the 
whole,  than  either  alcohol  or  tobacco,  caffeine  has  come 
into  general  use  in  much  the  same  way  as  these  substances. 
In  a  sense,  however,  caffeine  is  more  deceptive  than  either 
alcohol  or  nicotine,  because  the  usual  mode  of  preparing 
tea  and  coffee  gives  them  the  appearance  of  real  foods. 
The  housewife  who  would  feel  condemned  in  purchasing 
caffeine  put  up  as  a  drug  somehow  feels  justified  when 
she  extracts  it  from  plant  products  in  the  regular  prepara- 
tion of  the  meal. 

Counts  against  Caffeine.  —  People  of  vigorous  constitu- 
tions and  of  active  outdoor  habits  are  injured  but  slightly, 
if  at  all,  by  either  tea  or  coffee  when  these  are  used  in 
moderation.  As  already  stated  (pages  56,  167,  326,  329), 
they  do  harm  when  used  to  excess  and,  in  special  cases,  in 
very  small  amounts,  in  one  of  the  following  ways :  — 

1.  By  stimulating  the  nervous  system,  thereby  causing 
nervousness  and  insomnia  and  interfering  with  vital  organs. 

2.  By  introducing  a  waste  which  forms  uric  acid  into 
the  body,  thereby  throwing   an   extra  burden   upon   the 
organs  of  elimination. 

In  this  connection  it  may  also  be  stated  that  there  ap- 
pears to  be  little,  if  any,  real  advantage  to  the  healthy 
body  from  the  use  of  either  tea  or  coffee,  beyond  that  of 
temporary  stimulation  and  the  gratification  of  an  appetite 
artificially  acquired.  Hence  the  large  sums  of  money 
expended  for  these  substances  in  this  country  yield  no 
adequate  returns. 

Caffeine  Restrictions  Necessary.  —  Though  with  many  the 
cup  of  tea  or  coffee  at  breakfast  does  no  harm,  but  gives 
an  added  pleasure  to  the  meal,  there  is  no  question  but 
that  the  use  of  caffeine  beverages  should  be  greatly  cur- 
tailed. Children  should  not  be  permitted  to  drink  either 


4l8  PRACTICAL    HYGIENE 

tea  or  coffee.  Brain  workers  and  indoor  dwellers  generally 
should  use  these  substances  very  sparingly,  and  people 
having  a  tendency  to  indigestion,  nervousness,  constipation, 
rheumatism,  or  diseases  of  the  heart,  kidneys,  or  liver  fre- 
quently find  it  best  to  omit  them  altogether. 

Caffeine  and  "Soft"  Drinks.  —  Recently  the  practice 
has  sprung  up  of  using  caffeine  as  a  constituent  of  certain 
drinks  supplied  at  the  soda-water  fountains.  Such  drinks 
usually  purport  to  be  made  from  the  kola  nut,  which  con- 
tains caffeine,  or  to  consist  of  extracts  from  the  plants 
which  yield  cocoa  and  chocolate,  when  in  reality  they  con- 
sist of  artificial  mixtures  to  which  caffeine  has  been  added. 
Those  using  these  beverages  are  stimulated  as  they  would 
be  by  tea  or  coffee  and  soon  acquire  the  habit  which  makes 
them  regular  customers.  Chief  harm  comes  to  the  chil- 
dren who  frequent  the  soda  fountains  and  to  those  who, 
on  account  of  constitutional  tendencies,  should  avoid  caf- 
feine in  all  of  its  forms.  It  is  generally  understood  that 
the  so-called  "  soft "  drinks  are  harmless.  If  this  reputa- 
tion is  to  be  maintained,  those  containing  caffeine  must 
be  excluded. 

Danger  from  Certain  Medicinal  Agents.  —  Among  the 
most  valuable  drugs  used  by  the  physician  in  the  treat- 
ment of  disease  are  several,  such  as  morphine,  chloral,  and 
cocaine,  which  possess  the  habit-forming  characteristic. 
Sad  indeed  are  the  cases  in  which  some  pernicious  drug 
habit  has  been  formed  through  the  reckless  administra- 
tion of  such  medicines.  Even  the  taking  of  such  a  drug 
as  quinine  as  a  "tonic"  tends  to  develop  a  dependence 
upon  stimulation  which  is  equivalent  to  a  habit.  In  the 
same  list  come  also  the  drugs  that  are  taken  to  relieve 
a  frequently  recurring  indisposition,  such  as  headache. 
The  so-called  headache  powders  are  most  harmful  in  their 


THE   GENERAL   PROBLEM   OF   KEEPING  WELL      419 

effects  upon  the  nervous  system  and  should  be  carefully 
avoided.1 

Stimulants  in  Health  Unnecessary.  —  Stimulants  have  been 
aptly  styled  "the  whips  of  the  nervous  system."  The  healthy 
nervous  system,  however,  like  the  well-disposed  and  well-fed 
horse,  needs  no  whip,  but  is  irritated  and  harmed  through 
its  use.  Even  in  periods  of  weakness  and  depression,  stimu- 
lants are  usually  not  called  for,  but  a  more  perfect  provision 
for  hygienic  needs.  Rest,  relaxation,  sleep,  proper  food,  and 
avoidance  of  irritation,  not  stimulants,  are  the  great  restorers 
of  the  nervous  system.  A  surplus  of  nervous  energy  gained 
through  natural  means  is  more  conducive  to  health  and  effec- 
tive work  than  any  result  that  can  possibly  be  secured  through 
drugs.  Then  withal  comes  the  satisfaction  of  knowing  that 
one  has  the  expression  of  his  real  self  in  the  way  in  which  he 
feels  and  in  what  he  accomplishes  —  not  a  "  whipped-up  "  con- 
dition that  must  be  paid  for  by  weakness  or  suffering  later  on. 

Summary.  —  To  solve  the  problem  of  keeping  well,  one 
must  live  the  life  which  is  in  closest  harmony  with  the 
plan  of  the  body.  Such  a  life,  because  of  differences 
in  physical  organization,  as  well  as  differences  in  en- 
vironment and  occupation,  cannot  be  the  same  for  all. 
All,  however,  may  observe  the  conditions  under  which  the 
body  can  be  used  without  injuring  it  and  the  special 
hygienic  laws  relative  to  the  care  of  different  organs. 
Causes  of  disease,  whether  they  be  in  one's  environment, 
vocation,  in  his  use  of  foods  or  drugs,  or  in  his  mode  of 
recreation,  must  either  be  avoided  or  counteracted. 

While  the  problem  is  beset  with  such  difficulties  as  lack  of 
sufficient  knowledge,  inherited  weakness,  and  time  and  op- 

i  Most  headaches  are  the  result  either  of  eye  strain  or  of  digestive  disturbances, 
such  as  indigestion  and  constipation,  and  are  to  be  relieved  through  the  work  of 
the  oculist  or  through  attention  to  the  hygiene  of  the  digestive  system. 


420  PRACTICAL   HYGIENE 

portunity  for  doing  what  is  known  to  be  best  for  the  body, 
yet  study  and  work  that  have  for  their  aim  the  preserva- 
tion or  improvement  of  the  health  are  always  worth  while. 
Health  is  its  own  reward.  The  expression  of  the  poet, 

"  Each  morn  to  feel  a  fresh  delight  to  wake  to  life, 

To  rise  with  bounding  pulse  to  meet  whate'er  of  work,  of  care,  of  strife, 
day  brings  to  me," 

suggests  the  joy  of  being  well.  But  the  ultimate  realiza- 
tion of  one's  aims  and  ambitions  in  life  and  the  actual 
prolongation  of  one's  period  of  usefulness  are  higJicr  and 
more  enduring  rewards. 

Exercises. —  i.    Summarize    the   different  laws  of  hygiene.      Upon 
what  one  fundamental  law  are  these  based  ? 

2.  State  the  important  differences  between  a  condition  of  health 
and  one  of  disease. 

3.  In  what  general  ways  may  disease  originate  in  the  body  ? 

4.  Describe  a  model  sanitary  home.     With  what  special  hygienic 
problems  has  the  housekeeper  to  deal  ? 

5.  Describe  a  method  of  collecting  a  wholesome  supply  of  cistern 
water.     State  possible  objections  to  well  and  spring  water. 

6.  What  means  may  be  employed  in  preventing  the  spread  of  con- 
tagious diseases  ? 

7.  By  what  means  are  malaria,  typhoid  fever,  diphtheria,  and  tuber- 
culosis spread  from  one  individual  to  another  ? 

8.  Why  are  extra  precautions  necessary  in  the  recovery  from  certain 
diseases,  as  typhoid  fever,  diphtheria,  and  scarlet  fever  ? 

9.  How  may  one's  vocation  become  a  cause  of  disease  ?     What 
conditions  in  the  life  of  a  student  may,  if  uncounteracted,  lead  to  poor 
health  ? 

10.  Of  what  special  value  are  the  parks  and  pleasure  grounds  in  a 
city  to  the  health  of  its  inhabitants  ? 

11.  Discuss  the  hygienic  value  of  work. 

12.  What  conditions  lead  to  the  continuance  of  habit-forming  sub- 
stances after  their  use  has  become  general  ? 

13.  How  is  it  possible  for  one  not  using  alcohol  to  be  injured  by 
this  substance  ? 

14.  Discuss  the  effect  of  alcoholic  abuse  upon  social  environment. 

15.  Summarize  the  rewards  of  hygienic  living. 


SUMMARY   OF   PART   II  421 

SUMMARY   OF   PART   II 

For  the  maintenance  of  life  the  needs  of  the  cells  must 
be  supplied  and  the  body  as  a  whole  must  be  brought  into 
proper  relations  with  its  surroundings.  The  last-named 
condition  requires  that  the  body  be  moved  from  place  to 
place ;  that  its  parts  be  controlled  and  coordinated ;  and 
that  it  be  adjusted  in  its  various  activities  to  external  phys- 
ical conditions.  To  accomplish  these  results  there  are 
employed : 

1.  The  skeleton,  or  bony  framework,  which  preserves 
the  form  of  the  body  and  supplies  a  number  of  mechani- 
cal devices,  or  machines,  for  causing  a  variety  of  special 
movements. 

2.  The   muscular   system,  which   supplies   the   energy 
necessary  for  executing  the  movements  of  the  body. 

3.  The  nervous  system,  which  (a)  controls  and  coordi- 
nates the  various  activities  and  (#)  provides  for  the  intelli- 
gent adjustment  of  the  body  to  its  environment.     (Review 
Summary  of  Part  I,  page  215,  and  consult  Fig.  92,  page 
214.) 


APPENDIX 

Equipment.  —  Nearly  all  of  the  apparatus  and  materials  called  for  in 
this  book  may  be  found  in  the  physical,  chemical,  and  biological  labora- 
tories of  the  average  high  school.  There  should  be  ready,  however,  for 
frequent  and  convenient  use,  the  following :  One  or  more  compound 
microscopes  with  two-thirds  and  one-fifth  inch  objectives;  a  set  of  pre- 
pared and  mounted  slides  of  the  various  tissues  of  the  body ;  a  set  of 
dissecting  instruments,  including  bone  forceps ;  a  mounted  human 
skeleton  and  a  manikin  or  a  set  of  physiological  charts  ;  a  set  of  simple 
chemical  apparatus  including  bottles,  flasks,  test  tubes,  and  evaporating 
dishes  ;  and  a  Bunsen  burner  or  some  other  means  of  supplying  heat. 

The  few  chemicals  required  may  be  obtained  from  a  drug  store  or 
from  the  chemical  laboratory.  Access  to  a  work  bench  having  a  set  of 
carpenter's  tools  will  enable  one  to  prepare  many  simple  pieces  of  appa- 
ratus as  they  are  needed. 

Physiological  Charts  are  easily  prepared  by  teachers  or  pupils  by  care- 
fully enlarging  the  more  important  illustrations  found  in  text-books  or 
by  working  out  original  sketches  and  diagrams.  These,  if  drawn  on 
heavy  Manila  paper,  may  be  hung  on  the  wall  as  needed  and  preserved 
indefinitely.  By  the  use  of  colors,  necessary  contrasts  are  drawn  and 
emphasis  placed  on  parts  as  desired.  The  author  has  for  a  number  of 
years  used  such  home-made  charts  in  his  teaching  and  has  found  them 
quite  satisfactory.  His  plan  has  been  to  draw  on  heavy  Manila  paper, 
cut  in  sizes  of  two  by  three  feet,  the  general  outline  in  pencil  and 
then  to  mark  over  this  with  the  desired  colors.  There  is  of  course  an 
opportunity  for  producing  results  that  are  artistic  as  well  as  practical, 
and  if  one  has  time  and  artistic  skill,  better  results  can  be  obtained. 
Many  of  the  cuts  in  this  book  are  excellently  suited  to  enlargement  and, 
if  properly  executed,  will  provide  a  good  set  for  general  class  purposes. 

Models.  —  The  use  of  prepared  models  of  the  different  bodily  organs 
is  strongly  urged.  These  may  be  so  used  in  elementary  courses  as  to 
obviate  much  of  the  dissections  upon  lower  animals.  Although  the 
actual  tissues  cannot  be  so  well  portrayed,  the  general  form  and  con- 
struction of  organs  are  much  better  shown.  Models  well  adapted  to 
class  or  laboratory  work  are  easily  obtained  through  supply  houses. 
Illustrations  of  several  of  these  are  shown  in  connection  with  the  "  Prac- 
tical Work." 

422 


INDEX 


Abdomen,  dissection  of,  169. 
Abdominal  cavity,  7,  138,  153. 
Absorption,  173-186. 

Defined,  18,  173. 
Accommodation,  379. 

To  illustrate,  391. 
Acid  reactions,  171. 
Acquired  reflexes,  314. 
Adipose  tissue,  5,  178. 
Afferent  neurons,  296. 
Air,  76. 

Changes  it  undergoes  in  lungs,  101. 

Complemental,  89,  103. 

Reserve,  89,  103. 

Residual,  89,  103. 

Tidal,  88,  103. 
Air  passages,  80. 
Albuminoids,  119. 

Purpose  served  by,  121. 
Alcohol, 

A  cause  of  crime,  333. 

Effects  on  circulation,  55,  56. 

Effects  on  digestion,  167. 

Effects  on  energy  supply,  195. 

Effects  on  respiratory  organs,  98. 

Effects  on  social  environment,  413. 

Effect  on  temperature  regulation,  271. 

Effects  on  waste  elimination,  212. 

General  considerations,  412-415. 
Alimentary  canal,  coats  of,  138. 
Alimentary  muscles,  work  of,  159. 
Alkaline  reactions,  171. 
Alveoli,  82. 
Amylopsin,  155,  156. 
Anatomy,  defined,  i. 
Animal  heat,  192. 
Anopheles,  401. 
Antiseptic  ointment,  275. 
Antitoxin,  405. 
Appetite,  natural,  163. 
Aqueous  humor,  377. 


Arachnoid,  299. 
Arteries,  47. 

Bronchial,  84. 

Functions  of,  51. 

Pulmonary,  84. 

Renal,  202. 

To  illustrate  elasticity  of,  62. 

Why  elastic,  48. 
Articulations,  230-232. 

Kinds  of,  230. 
Assimilation,  18,  182. 
Astigmatism,  384. 
Atlas,  223. 
Atoms,  defined,  105. 
Attraction  sphere,  15. 
Auditory  canal,  358. 
Auricles,  42. 
Axis,  223. 
Axis  cylinder,  284. 
Axon,  283. 

Form  and  length  of,  284. 

Function  of,  306. 

Structure  of,  284. 

Bacteria,  394. 
Ball-and-socket  joint,  231. 
Basement  membrane,  197. 
Basilar  membrane,  363. 
Bathing,  272,  274. 
Biceps  muscle,  action  of,  263. 
Bicuspids,  143. 
Bile,  154,  155. 
Binocular  vision,  381. 
Blind  spot,  377. 

To  prove  presence  of,  390. 
Blood,  24-39. 

Changes  in,  34. 

Checking  flow  from  wounds,  58. 
'  Coagulation  of,  31. 

Experiments  with,  37-39- 

Flow  of,  how  regulated,  50. 


423 


424 


INDEX 


Blood  (continued). 

Functions  of,  33. 

Hygiene  of,  34-36. 

Physical  properties  of,  24. 

Quantity  of,  33. 

Supply  to  lungs,  82. 

Velocity  of,  54. 

Where  found,  24. 
Blood  platelets,  25. 
Blood  pressure,  52,  70. 
Blood  pressure  and  velocity,  52. 
Blood  vessels,  to  strengthen,  57. 
Body,  organization  of,  19. 
Bone  groups,  223-229. 
Bones,  216-242. 

Adaptation  of,  228. 

Composition,  217. 

Gross  structure  of,  218. 

Minute  structure  of,  219. 

Observation  on  gross  structure,  241. 

Properties  of,  217. 

Table  of,  229. 

To  show  composition  of,  241. 

To  show  minute  structure  of,  242. 
Bowels,  rules  for  care  of,  166. 
Brachial  plexus,  302. 
Brain,  280,  288-291. 

Disturbed  circulation,  327. 

Protection  of,  299. 
Brain  workers,  408. 
Breathing,  see  Respiration. 

Causes  of  shallow,  92. 

Illustrated,  87. 

To  prevent  shallow,  92. 
Breathing  exercises,  93. 
Bronchus,  80. 
Bulb,  291. 

Caecum,  151,  158. 
Calcium  carbonate,  122. 
Calcium  phosphate,  122. 
Calorie,  defined,  127. 
Cane  sugar,  120. 
Canines,  143. 
Capillaries,  50,  64,  249. 

Blood  pressure  at,  70. 

Functions  of,  51. 

Work  of,  174. 
Carbohydrates,  119,  125. 

Purpose  served  by,  121. 


Storage  of,  177. 

Tests  for,  135. 
Carbon,  134. 
Carbon  dioxide, 

Final  disposition  of,  in. 

Preparation,  115. 

Pressure,  no. 

Properties,  no,  115. 
Cardiac  cycle,  46. 
Cardiac  orifice,  147. 
Carpals,  227. 
Carpus,  228. 
Cell  body,  283. 

Functions  of,  305. 
Cell-division,  16. 
Cell  nucleus,  14. 
Cell  reproduction,  16." 
Cell  structure,  14. 
Cell  surroundings,  17. 
Cell  wall,  15. 
Cells,  13-23. 

Bone,  how  nourished,  220. 

Ciliated  epithelial,  81. 

Food  supply  to,  180. 

General  work  of,  17. 

Importance  of,  15. 

Passage  of  materials  to,  183. 

Relation  to  nutrient  fluid,  20. 

Specialized,  197. 

Special  work  of,  18. 

Striated  muscle,  244. 
Cerebellum,  290. 

Functions  of,  317. 

Cerebral  functions,  localization  of,  318. 
Cerebral  hemispheres,  289. 
Cerebral  peduncles,  290. 
Cerebrum,  288. 

Functions  of,  317. 
Chlorine,  135. 
Cholesterine,  155. 
Chordae  tendineae,  43. 
Choroid  coat,  375. 
Chyme,  150. 
Cigarettes,  333. 
Cilia,  81. 

To  observe,  101. 
Ciliary  muscle,  375. 
Ciliary  processes,  375. 
Circulation  of  blood,  40-64. 

Causes  of,  54. 


INDEX 


425 


Circulation  of  blood  (continued). 

Discovery  of,  by  Harvey,  40. 

Divisions  of,  51,  52. 

Effects  of  exercise  upon,  63. 

Effects  of  gravity  upon,  64. 

In  a  frog's  foot,  64. 

Organs  of,  40-54. 

Routes  to,  174. 
Coagulation, 

Causes  of,  31. 

Purpose  of,  32. 

Time  required  for,  33. 
Cochlea,  362. 
Coffee, 

Effects  on  complexion,  274. 

Effects  on  digestion,  167. 

Effects  on  heart,  56. 
Colds,  193. 

Serious  nature  of,  94. 

To  cure,  94. 
Colon,  parts  of,  158. 
Complexion,  care  of,  273. 
Compound,  defined,  104. 
Conduction  pathways,  286. 
Conductivity,  304. 
Condyloid  joint,  232. 
Conjunctiva,  373. 
Consumption,  see  Tuberculosis.. 
Control  of  arteries,  319. 
Convolutions,  289. 
Coordination,  defined,  279. 
Cornea,  375. 

Corpora  quadrigemina,  290. 
Corpora  striata,  289. 
Corpus  callosum,  289,  293. 
Cortex,  288,  294. 
Coughing,  81. 
Cranial  cavity,  7,  225. 
Cranial  nerves,  296. 
Crura  cerebri,  290. 
Crystalline  lens,  380. 
Culex,  402. 
Cytoplasm,  15. 

Defects  in  focusing,  383. 
Deformities  of  skeleton,  233-236. 

Correction  of,  236. 

Prevention  of,  235. 
Deglutition,  145. 

Steps  in,  146. 


Dendrites,  283,  306. 
Dentine,  143. 
Dermis,  264. 
Dextrose,  30,  120,  150. 
Diaphragm,  88. 

To  illustrate  action  of,  loa. 
Diastole,  46. 
Diaxonic  neuron,  283. 
Diet,  one-sided,  124. 
Diffusion,  371. 
Digestion,  130-172. 

Hygiene  of,  160. 

Nature  of,  130. 

Not  a  simple  process,  131. 

Of  fat,  156. 

Purpose  of,  177. 

Stomach,  148. 
Digestive  fluids,  132. 
Digestive  organs,  160. 

Table  of,  138. 
Digestive  processes,  130,  141. 

Illustrated,  137. 
Diphtheria,  94,  405. 

Care  after,  211. 
Disaccharides,  120. 
Disease,  392-412. 

Causes  of,  393. 

Eruptive,  405. 

Precautions  in  recovery  from,  407. 

Prevention  of,  393. 
Dislocations,  239. 
Dorsal-root  ganglia,  295. 
Drill,  "  setting  up,"  237. 
Drugs,  effects  of,  35,  55, 129,  332. 
Duodenum,  151. 
Dura,  299. 

Ear,  358. 

Hygiene  of,  365. 

To  demonstrate,  369. 
Ear  drum,  359. 
Efferent  neurons,  296. 
Element,  defined,  104. 
Elevators  of  the  ribs,  87. 
Emetics,  151. 

Emotional  states,  effects  of,  330. 
End  bulbs,  342. 
Endocardium,  42. 
Endolymph,  361. 
End-plate,  244. 


426 


INDEX 


End-to-end  connections,  286. 
Energy,  107,  186-196. 

Bodily  control  of,  192. 

From  sun  to  cells,  191. 

How  plants  store  sun's,  189. 

Increasing  one's  bodily,  194. 

In  food  and  oxygen,  190. 

Kinds  of,  186. 

Methods  of  storing,  187,  188. 

Transformation  of,  in  muscle,  248,  249. 
Enzymes,  132,  155. 

Of  the  tissues,  184. 
Epidermis,  264,  266. 
Epiglottis,  80,  354. 
Epithelium,  139. 
Eruptive  diseases,  405. 
Esophagus,  146. 
Eustachian  tube,  359. 
Excessive  reading,  331. 
Excitant  impulse,  305. 
Excretion,  197-213. 

Defined,  18. 

Necessity  for,  201. 
Exercise,  256,  257,  328,  409. 

General  rules  for,  259. 

Results  of,  257. 
Exhaustion,  nervous,  211. 

Results  of,  195. 
External  ear,  358. 
External  stimuli,  action  of,  307. 
Eye,  370-391. 
Eyeball,  373. . 

Chambers  of,  377. 

Focusing  power  of,  378. 

Movements  of,  381. 
Eyelids,  373. 
Eyes, 

Care  of,  386. 

Removal  of  foreign  bodies  from,  387. 

Strong  chemicals  in,  388. 
Eye  strain,  211. 

And  disease,  385. 

Fat,  30,  149,  162. 
Digestion  of,  156. 
Emulsification  of,  157. 
Purpose  served  by,  121. 
Route  taken  by,  175. 
Tests  for,  137. 
Where  stored,  178. 


Fatty  acid,  156. 
Fenestra  ovalis,  361. 
Fenestra  rotunda,  363. 
Ferments,  see  Enzymes. 
Fibrin,  31. 
Fibrin  ferment,  32. 
Fibrinogen,  30,  31. 
Fissures,  289. 
Food,  117-137. 

Advantages  of  coarse,  167. 

Classes  of,  118,  119. 

Composition  of,  124. 

Dangers  from  impure,  165. 

Defined,  117. 

Elements  supplied  by,  134. 

Excess  of  proteid,  209. 

Frequency  of  taking,  165. 

Materials,  table  of,  126,  127. 

Nitrogenous,  119. 

Order  of  taking,  161. 

Preparation  of,  164. 

Purity  of,  ic8. 

Quantity  of,  164. 

Simple,  118. 

Variety,  128. 

With  reference  to  digestive  changes 

132. 

Foot  lever,  diagram  of,  253. 
Foot-pound,  196. 
Foot-wear,  hygienic,  238. 
Fractures,  treatment  of,  239. 
Fumigation,  400. 
Furniture,  school,  236. 

Gall  bladder,  154. 
Ganglia,  281. 

Dorsal-root,  295. 

Sympathetic,  298. 
Gastric  glands,  147. 

Gastric  juice,  to  illustrate  action  of,  172. 
Gelatine,  218. 

Germ  diseases,  avoidance  of,  394. 
Germs,  29,  394,  395. 

How  spread,  395. 
Glands,  197-213. 

Digestive,  140. 

Ductless,  208. 

Excretory,  work  of,  201. 

Gastric,  147. 

Kinds  of,  197,  198. 


INDEX 


427 


Glands  {continued). 

Lymphatic,  68,  208. 

Perspiratory,  206. 

Salivary,  144. 

Structure  of,  197. 

Thymus,  208. 

Thyroid,  208. 
Gliding  joint,  232. 
Glottis,  355. 
Glycogen,  120,  177. 
Grape  sugar,  tests  for,  120,  136. 
Gross  anatomy,  defined,  i. 
Gal  let,  146. 
Gustatory  pore,  345. 
Gustatory  stimulus,  345. 

Habits,  315,  334. 
Hair,  267. 

Care  of,  276. 
Hair  cells,  363. 
Hair  follicle,  267. 
Haversian  canals,  219. 
Hearing,  defective,  366. 
Heart,  41. 

Care  of,  55. 

Connection  with  arteries  and'vems,45, 

Difference  in  parts  of,  44. 

How  it  does  its  work,  45. 

Observations  on,  60,  61,  62. 

Sounds  of  the,  47. 

Valves  of,  43. 

Heart  muscle,  structure  of,  247. 
Heat  and  cold,  effects  of,  330. 
Hemoglobin,  26. 
Hepatic  artery,  154. 
Hepatic  veins,  154. 
Hindbrain,  290. 
Hinge  joint,  231. 
Histology,  defined,  I. 
Humerus,  227. 
Hyaloid  membrane,  378. 
Hydrochloric  acid,  149,  150. 
Hydrogen,  134. 
Hygiene, 

Defined,  2. 

General  aim  of,  2. 

General  laws  of,  2,  392. 

Of  digestion,  160. 

Of  skeleton,  238. 

Relation  of  physiology  and  anatomy  to,  3- 


Hygienic  housekeeping,  399. 
Hypoglossal  nerves,  298. 

Ileo-ceecal  valve,  151. 
Ileum,  151. 
Images, 

Diagram  illustrating,  372. 

Formation  of,  371. 
Incisors,  143. 
Incus,  359. 

Infectious  diseases,  394. 
Infundibula,  80,  84. 
Inhibitory  impulse,  305. 
Insomnia,  329. 
Inspiratory  force,  70. 
Intercellular  material,  production  of,  13, 

18. 

Internal  ear,  360. 
Intestinal  juice,  152,  157. 
Iris,  375. 
Iron,  135. 

!rritability,6,  243,  304. 
Isolation,  406. 

Jejunum,  151. 
^oints,  230-232,  242. 

Sidneys,  201. 

Blood  supply  to,  204. 

Cortex  of,  204. 

Inflammation  of,  211. 

Pelvis  of,  202. 

Structure,  202. 

Symptoms  of  diseased,  211. 

Work  of,  205. 
Cnee  jerk  reflex,  322. 

-achrymal  glands,  383. 
^acteals,  work  of,  174.  * 
.acunae,  220. 
_,aminae,  220. 
^arge  intestine,  157. 

Division  of,  158. 

Work  of,  159. 
.arynx,  80,  353-357- 

To  show  plan  of,  368. 
^ever,  251. 

Application  to  the  body,  251. 

Classes  of,  in  body,  251. 

Producing  motion,  diagram  of,  252. 

To  show  action  of,  252. 


428 


INDEX 


Leucocytes,  27. 
Levulose,  120,  150. 
Life,  maintenance  of,  20. 
Light,  370,  371. 

Simple  properties,  illustrated,  389. 
Light  waves,  diagram  illustrating  passage 

of,  370. 

Lime  water,  to  prepare,  101. 
Liver,  52,  152-155,  178. 

Protection  of,  216. 

Work  of,  206. 
Lockjaw,  276. 
Longsightedness,  384. 
Lung  capacity,  diagram  illustrating,  89. 
Lung  diseases,  out-door  cure  for,  98. 
Lungs,  77-103. 

Capacity  of,  88. 

Changes  air  undergoes  in,  101. 

Excretory  work  of,  207. 

Interchange  of  gases  in,  88. 

Observations  of,  100. 

Supply  of  blood  to,  82. 

To  estimate  capacity  of,  103. 

Weakest  portions  of,  92. 
Lymph,  65-75. 

Composition,  66. 

Movements  at  the  cells,  71. 

Origin  of,  65. 

Physical  properties,  66. 

Where  it  enters  the  blood,  70. 
Lymph  movements,  causes  of,  69. 
Lymph  spaces,  66. 
Lymph  vessels,  66. 

Variable  pressure  on  the  walls  of,  70. 

Magnesium,  135. 
Malarial  fever,  401. 
Malleus,  359. 
Malpighian  capsules,  203. 
Maltose,  120. 
Massage,  259. 
Mastication, 

Muscles  of,  144. 

Slow,  145. 

Thorough,  160. 

To  show  importance  of,  171. 
Matrix,  267. 
Measles,  94. 

Care  after,  211. 
Median  fissures,  289. 


Medulla  oblongata,  291. 
Medullary  sheath,  284. 
Membrana  tympani,  358. 
Membrane, 

Active,  173. 

Basement,  197. 

Basilar,  363. 

Membranous  capsule,  377. 
Membranous  labyrinth,  361. 
Mesentery,  152. 
Metacarpals,  227. 
Midbrain,  289. 
Middle  ear,  359. 

Purposes  of,  360. 
Milk  sugar,  120. 
Mineral  salts,  30. 

Uses,  121. 

Moderate  drinkers,  333. 
Molars,  143. 
Molecules,  defined,  105. 
Mon-axonic  neuron,  diagram  of,  282. 
Mono-saccharides,  120. 
Mosquitoes,  401-403. 

Remedies  against,  402. 
Mouth,  141. 
Movable  joints, 

Kinds  of,  231. 

Structure  of,  230. 
Mucous  membrane,  80,  264. 
Mucus,  139. 
Muscle  organ,  245. 
Muscles,  243-263. 

Alimentary,  189. 

Important,  254-256. 

Intercostal,  87. 

Of  mastication,  144. 

Properties  of,  243. 
Muscular  force,  plan  of  using,  249. 
Muscular  sensations,  344. 
Muscular  stimulus,  248. 
Muscular  stimulus   and   contraction,  to 

illustrate,  261. 
Muscular  tissue,  kinds  of,  243,  244. 

Nails,  267. 

Care  of,  276. 
Nasal  duct,  383. 
Neck  exercise,  328. 
Nerve  cells,  281,  282. 
Nerve  fibers,  282,  293,  294. 


INDEX 


429 


Nerve  path,  diagram  of,  286. 

Nerve  pathways,  to  demonstrate,  322. 

Nerves,  281. 

Nerve  skeleton,  280. 

Diagram  of,  281. 
Nerve  stimuli,  306. 
Nerve  trunks,  281. 

Nervous  activity,  wasteful  forms  of,  325. 
.Nervous  control  of, 

Body  temperature,  320. 

Circulation  of  blood,  318. 

Respiration,  320. 

Nervous  energy,  economizing  of,  315. 
Nervous  impulse,  248,  305. 
Nervousness,  326. 
Nervous  system,  279-337. 

Diagram  of,  287. 

Dissection  of,  302. 

Divisions  of,  287. 

Hygiene  of,  324-337. 

Nature  of,  287. 

Physiology  of,  304-323. 

Work  of,  280. 
Neural  arch,  224. 
Neurilemma,  284. 
Neurons,  281,  282. 

Arrangement  of,  284,  293. 

Diagram,  illustrating,  285. 

Properties  of,  304. 
Nicotine, 

Effects  of,  333. 

Relation  of  age  to  effects,  333. 
Nitrogen,  134. 

Non-striated  cells,  to  show,  261. 
Non-striated  muscles, 

Purpose  of,  246. 

Structure  of,  246. 

Work  of,  247. 
Normal  temperature,  269. 
Nosebleed,  58. 
Nucleoplasm,  14. 
Nutrients  (see  Foods), 

Composition  of,  135. 

Relative  quantity  needed,  123. 

Routes  taken  by,  175. 

Tests  for,  136. 
Nutriment,  storage  of,  177-180. 

Olfactory  stimulus,  347. 
Opsonins,  34. 


Optic  thalami,  289. 
Orbit,  373. 
Organ,  defined,   7. 
Organism,  denned,  19. 
Organization,  denned,  10. 
Osmosis,  72. 

At  the  cells,  72. 

To  illustrate,  75. 
Ossein,  218. 
Overstudy,  211. 
Oxidation,  defined,  106. 
Oxygen,  104-117. 

Combined,  105,  113. 

Free,  105,  113. 

How  it  unites,  105. 

Main  uses  of,  108. 

Movement  a  necessity,  106,  108,  115. 

Movement  in  body,  106,  108,  115, 

Nature  of,  104. 

Passage  of,  from  cells,  no. 

Passage  of,  through  blood,  109. 

Passage  of,  toward  cells,  109. 

Preparation  of,  113. 

Pressure,  109. 

Properties  of,  113. 

Purpose  of,  in  the  body,  106. 
Oxyhemoglobin,  27. 

Pacinian  corpuscles,  342,  343. 

To  demonstrate,  348. 
Pancreas,  155. 
Pancreatic  juice,  155. 
Papillae,  266. 

Patent  medicines,  166.         , 
Pelvic  girdle,  226. 
Pepsin,  149. 
Peptones,  149,  176. 
Pericardium,  41. 
Perilymph,  361. 
Perimysium,  245. 
Periosteum,  218. 
Peritoneum,  180. 
Perspiration,  207. 
Pharynx,  145. 

Openings  into,  145,  146. 
Phosphorus,  135. 
Phrenic.nerve,  302. 
Physiological  salt  solution,  38. 
Physiology,  defined,  2. 
Pia,  299. 


430 


INDEX 


Pigment  granules,  266. 
Pinna,  358. 

Pitch,  detection  of,  365. 
Pivot  joint,  232. 
Plasma,  25,  29. 
Pleura,  84. 
Plexus,  281. 
Pneumonia,  94. 
Pons,  290. 
Pons  Varolii,  290. 
Portal  vein,  154. 
Primitive  sheath,  284. 
Proteids,  161. 

Circulating,  179. 

Kinds  of,  118. 

Purposes  of,  119. 

Supplied  by,  125. 

Tests  for,  135,  136. 

Tissue,  179. 
Proteoses,  149,  176. 
Protoplasm,  14. 
Protozoa,  394. 
Ptyalin,  145. 
Public  sanitation,  396. 
Pulp  cavity,  143. 
Pupil,  375. 
Pure  food  law,  128. 
Pus,  28,  29. 
Pyloric  orifice,  147. 
Pyramids,  202. 

Quarantine,  406. 

Radius,  227^ 

Reaction  time,  to  determine,  323. 

Reading  glasses,  386. 

Receptacle  of  the  chyle,  68,  170. 

Rectum,  158. 

Red  corpuscles,  25. 

Disappearance  of,  27. 

Function  of,  26. 

Origin  of,  27. 

To  examine,  38. 

To  prepare  models  of,  39. 
Red  marrow,  219. 

Reenforcement  of  sound,  352,  356,  368. 
Reflection,  kinds  of,  371. 
Reflex  action,  308. 

Diagram  illustrating,  310. 

In  circulation  of  blood,  311. 


In  digestion,  310. 

Purposes  of,  311. 
Reflex  action  and  mind,  308. 
Reflex  action  pathway,  309. 
Refraction,  371. 
Rennin,  149. 
Respiration,  76-103. 

Artificial,  97. 

Internal,  89. 

Lung,  76. 
Retina,  376. 
Retiniris,  333. 
Rheumatism, 

Effects  on  the  heart,  56. 

Sequel  to  other  diseases,  407. 
Right  lymphatic  duct,  67. 
Rods  and  cones,  377. 
Rods  of  Corti,  364. 

Sacrum,  224. 
Saliva,  145. 

Composition  of,  145. 

Uses  of,  145. 

To  show  action  on  starch,  171. 
Salivary  glands,  144. 

Kinds  of,  144. 

Reflex  action  of,  323. 
Sanitation,  defined,  2. 
Sarcolemma,  244. 
Sarcoplasm,  244. 
Scala  media,  363. 
Scala  tympani,  363. 
Scala  vestibula,  363. 
Scarlet  fever,  care  after,  211. 
Sciatic  nerve,  302. 
Sclerotic  coat,  374. 
Secondary  reflex  action,  314. 
Secretions,  197. 

Kinds  of,  200. 

Secretory  process,  nature  of,  199. 
Seeing,  problem  of,  372. 
Self-control;  326,  334. 

Habit  of,  325. 
Semicircular  canals,  362. 
Semilunar  valves,  44. 
Sensations,  338-349. 

Classes  of,  339. 

Production  of,  338,  349. 

Purposes  of,  340. 

Special,  340. 


INDEX 


431 


Sensations  (continued). 

Steps  in  production  of,  341. 
Sensation  stimuli,  339. 
Sense  organs,  simple  forms  of,  341,  342. 
Serous  coat,  140,  148. 
Serous  membrane,  264. 
Serum  albumin,  30. 
Serum  globulin,  30. 
Shortsightedness,  384. 
Shoulder  girdle,  226. 
Sight,  organs  of,  373. 
Sigmoid  flexure,  158. 
Simple  life,  410. 
Skeleton,  216-243. 
How  deformed,  234. 
Hygiene  of,  233. 
Plan  of,  221. 
Purpose  of,  221. 
Skin,  264-277. 

As  regulator  of  temperature,  270. 
Experiments  on,  349. 
Functions  of,  267,  268. 
Observations  on  skin,  278. 
Skin  wounds,  treatment  of,  275. 
Skull,  225. 
Sleep,  329. 
Small  intestine,  151. 

Mucous  membrane  of,  151. 
Muscular  coat  of,  152. 
As  organ  of  absorption,  173. 
Parts  of,  151. 
Serous  coat  of,  152. 
Work  of,  157. 
Smell, 

Sensation  of,  346. 
Value  of,  347. 
Sneezing,  81. 
Sodium,  135. 
Sodium  carbonate,  155. 
Sodium  chloride,  122. 
Soft  palate,  141. 
Solution,  131. 

Kinds  of,  73. 
Solution  theory,  156. 
Solvents,  131. 
Sound, 

To  illustrate  origin  of,  367. 
To  show  transmission  of,  367. 
Sound  waves, 
As  stimuli,  351. 


Nature  of,  350. 

Reenforcement  of,  352. 

To  show  effects  of,  368. 

Value  of,  353. 

Speech,  production  of,  357. 
Spinal  column,  223-225. 

Hygiene  of,  233. 
Spinal  cord,  280. 

Protection  of,  299. 
Spinal  nerves,  295. 

Double  nature  of,  295. 
Spitting,  403. 
Spleen,  208. 
Sprains,  239,  240. 
Stapes,  359. 
Starch,  162. 

Action  of,  on  saliva,  171. 

Animal,  120. 

Tests  for,  136. 
Steapsin,  155,  156. 
Stegomyia,  403. 
Sternum,  225. 
Stomach,  147. 

Mucous  membrane  of,  147. 

Muscular  action  of,  150. 

Muscular  coat,  148. 
Serous  coat,  148. 
Storage  of  nutriment,  177-179. 
"  Strenuous  life,"  410. 
Striated  fibers,  to  show,  261. 
Striated  muscles,  to  show,  261. 
Stroma,  25. 
Sugars,  kinds,  120. 
Sulphur,  135. 
Supra-renal  bodies,  208. 
Suspensory  ligament,  377. 
Sutures,  230. 
Sympathetic  ganglia  and  nerves,  298. 

Work  of,  316. 
Synovial  fluid,  231. 
Synovial  membrane,  231. 
System,  defined,  20. 
Systole,  46. 

Taste  buds,  345. 
Tea. 

Effects  on  digestion,  167. 

Effects  on  heart,  56. 
Tears,  383. 
Teeth,  142. 


432 


INDEX 


Teeth  (continued). 

Care  of,  163. 

Kinds  of,  143. 
Temperature, 

Body,  207. 

Corpuscles,  271,  345. 

Sensation,  343. 
Tendon  of  Achilles,  256. 
Tendons,  246. 
Tests  for  foods,  136,  137. 
Tetanus,  262,  275. 
Thoracic  cavity,  7,  85,  100,  102. 
Thoracic  duct,  67,  170. 
Thorax,  85. 

Bones  of,  225. 
Tissue  enzymes,  182. 
Tissues,  4. 

Complex  nature  of,  13. 

Denned,  20. 

General  purposes  of,  5. 

Kinds  of,  5,  6. 

Observations  on,  12. 

Properties  of,  6. 
Tobacco,  effect  on  heart,  56. 
"  Tobacco  heart,"  56,  333. 
Tongue,  143. 
Tonic  bath,  273. 
Touch,  343. 
Touch  corpuscles,  342. 
Toxins,  394. 
Trachea,  80. 
Trypsin,  155,  156. 
Tuberculosis,  90, 92,  94,  98. 

How  communicated,  403. 

Outdoor  treatment,  98. 

To  prevent,  404. 
Tympanum,  359. 
Typhoid  fever,  404,  407. 

Ulna,  227. 

Urea,  no,  205,  207,  210. 
Ureters,  170. 
Uriniferous  tubules,  203. 

Vaccination,  406. 
Valves, 
Advantages  of,  in  veins,  49,  63. 


Mitral,  43. 

Position  of,  in  veins,  63. 

Purposes  of,  49,  63. 

Tricuspid,  43. 
Veins,  47. 

Functions  of,  51. 

Renal,  202. 
Ventilation,  94. 

Rules  for,  95,  96. 
Ventricles,  42. 

To  illustrate  action  of,  62. 
Vermiform  appendix,  158. 
Vertebrae,  223-225. 

Interlocking  of,  225. 

Joining  of,  224. 

Kinds,  223. 
Vestibule,  361. 
Villi,  152. 

Parts  of,  173,  174. 
Visual  perceptions,  382. 
Visual  sensations,  382. 
Vitreous  humor,  378. 
Vocal  cords,  355. 
Voice,  353-357- 

How  produced,  356. 

Pitch  and  intensity,  356. 
Voluntary  action,  311,  312. 
Voluntary  action  pathways,  312. 
Vomiting,  151,  152. 

Waste  material,  passage  from  body,  210. 

Wastes,  30. 

Water, 

Importance  of,  123. 

Supply  of,  398. 

Value  of,  210. 
Water-vapor,  208. 
White  corpuscles,  27,  28. 

Functions  of,  29. 

To  examine,  39. 
Work, 

Hygienic  value  of,  328,  409. 
Worry,  211. 

Yellow  fever,  403. 
Yellow  marrow,  218. 
Yellow  spot,  377. 


UC  SOUTHERN  REGIONAL  LIBRARY  FACILITY 


A    000034820     1 


